My computer powers up but there is no signal to the monitor, have tried monitor and cables seperately and they are ok. how can i test the motherboard without a screen? have tried removing and repalcing the memory and the garphics card? Computer is a Medion MT6

We will assume the monitor you are using is ok. Check these items (in no particular order):
1. Bad RAM - remove and re-seat each module (you can take each one out and try to re-boot to see if it makes any difference)
2. Short circuit, usually between motherboard and case
3. Bad monitor cable (make sure it's not loose at either end)
4. Incorrect overclock setting
5. Bad display adapter (unless you added one, I believe this mother board has integrated video) - you can try adding an external video card if you have an open slot and and the PSU can take it.
6. Bad motherboard
7. CMOS battery - try replacing it, especially if it is over 6 years old
8. Overheating due to dirt collection inside - blow it out with canned air including the power supply unit (PSU)
9. Virus - not too likely

to start unplug monitor from power and from computer and test computer with different monitor to find out if it is monitoror computer fault.if it is computer fault and no video signal ,then test
-video cable
-video adapter on pc (sometimes integrated on motherboard).
-motherboard

Display Power management is being triggered because no input signal was detected. Verify that the video source is connected and on. (Computer, notebook, etc).
- Try another computer or laptop that you know is working properly.
- Do you see any change on the screen if the display cord is completely disconnected (often a "Test" or "Check Cable" message appears). - Inspect the signal cable from the monitor - worn? Any places where the cable was bent to an extremely small (acute) angle? (less than 75 degrees?) Try gently moving the cable around at either end and see if you get a partial signal on the screen (while connected to the computer). If you do, the signal cable is damaged, if possible replace it. try: www.monoprice.com

Replace the graphics card and test again or if you are using the built in graphics chip, try connecting to a seperate card. Check the cable to the monitor and also try a different monitor.

If that fails, the issue is likely to be with the motherboard and its components.
Possible causes to be investigated are:
Power supply PSU not working
CPU not working (see if the heatsink is getting warm)
Motherboard damaged ( only certain way to test is to replace the cpu with aknown good one, if the system fails to boot, the motherboard is damaged)
Try swapping the RAM modules, sometimes they fail halting the system

1) No. The switch color should have been Green

2) No Signal on the monitor, indicates the monitor is not receiving a Video Signal from the computer.

A) Could be due to a faulty monitor cable.
Monitor cable is used on a working computer for a test,
Or,
working computer's monitor cable is used on the Advent for a test.

B) Could be due to the graphics 'engine' on the motherboard, or on the graphics card is bad.

[Graphics 'engine'.
GPU
Graphics Processing Unit.

http://en.wikipedia.org/wiki/GPU ]

If the computer is using Integrated Graphics, the GPU is on the motherboard.

(Integrated Graphics is also referred to as OnBoard Graphics. Meaning On the motherBoard)

You will know if it's Integrated Graphics, because the monitor cable will be plugged into the VGA connector, on the motherboard

http://en.wikipedia.org/wiki/VGA_connector

Since you indicate an adapter was included, to adapt to a different port (Connector), it could be a VGA to DVI adapter, or a DVI to VGA adapter.

Your monitor may just have a VGA connector on the monitor cable.
Hence you would use a female VGA to Male DVI adapter.

Your monitor may be an LCD flat screen monitor, and has a DVI connector on the monitor cable.
Hence you would use a female DVI to Male VGA adapter.

DVI
Digital Visual Interface

http://en.wikipedia.org/wiki/Digital_Visual_Interface

VGA monitors are Analog.
LCD monitors are Digital.

A computer puts out a digital signal.

If a VGA monitor is used, the computer has to alter the Digital signal to an Analog one.
This slows down the video signal.

If your monitor (In any case. Not just this one), is an LCD flat screen monitor, it is best to use a DVI monitor cable, and plug into a DVI port on the computer, if available.

If your monitor is a VGA (CRT. Cathode Ray Tube), monitor, and you have a DVI connection on your computer, using the adapter will do you no good.

The adapter just uses the contact pins for VGA, that are present in that DVI adapter, and hence the DVI connection on the computer.

You're still just getting an Analog VGA signal.

Example of a female VGA to male DVI adapter,

http://www.directron.com/dvi.html

If the Integrated Graphics are suspected to be bad, a graphics card is used in the appropriate expansion slot, for a test.

If the graphics work then, the graphics card is left in service.

After I test the monitor cable my next procedure is to suspect the Power On switch, or the Power Supply, and go to the graphics next.

The reasoning is that Power Supply failure, is the number one cause of computer failure.
The next is the Power On switch, then Electrolytic Capacitors used on the motherboard.

(Specifically, any Electrolytic Capacitors used in the motherboard Voltage Regulator Circuit)

If the Power On switch is bypassed, the diagnosis will reveal if the problem is the switch, or Power Supply.

Bypass the Power On switch, and the Power Supply comes on?
Problem is the Power On switch.

[One Power On switch I have found to fit a lot of computers. The Power On switch goes into the plastic Power On button,

http://www.directron.com/atxswitch.html ]

Bypass the Power On switch, and the Power Supply does Not come on?
The problem is the Power Supply.

The Power On switch is bypassed using a jumper wire, from the green Soft Power On wire, to ANY black Ground wire. The contact made is a brief momentary one.

The jumper wire is used at the back, of the 20, or 24-pin ATX main power cable connector.

To be continued in an additional Comment.

It essentially means No Video Signal.

You are not receiving a video signal TO the monitor.
The monitor seems to be working A-OK.

Problem may be,

1) Bad monitor cable.

If the monitor cable is removable from the monitor, suggest use a monitor cable that is known to be good for a test. Perhaps one from a working computer, just borrowed for a test.

If the monitor cable is of the type that is not removable, try another known to be good monitor with cable, if available.

2) If this problem is listed in the correct category, and the desktop computer is a Gateway GT5404,

The GT5404 comes stock with Integrated Graphics. This is a graphics chip that is soldered to the motherboard.
(Another name for Integrated Graphics is OnBoard graphics. On the motherBoard)

The graphics chip is an Intel GMA 950. {Intel Graphics Media Accelerator]

This GPU is soldered to the motherboard.

[Chip and Chipset are slang terms for I.C. Integrated Circuit.
GPU stands for Graphics Processing Unit.
A type of 'Chip',

http://en.wikipedia.org/wiki/GPU ]

If this GPU is at fault, you'll receive no video signal.

You can use a video (Graphics) card to bypass using the Integrated Graphics, and have your graphics back.

(Don't forget to plug the monitor cable into the graphics card, not to the motherboard. Don't laugh! {Lol!} I've guided people who have done this)

The GT5404's, Intel (Coryville) 945G motherboard has a PCI-Express x16 slot for a graphics card.

Supporting data:

http://support.gateway.com/s/pc/R/1009371/1009371nv.shtml

Click on the heading - Specifications. Read down to the subheading - Add-in Card Slots.
One PCI Express x16 (graphics interface)
One PCI Express x1
Two PCI conventional.

Also go back to the main menu, and click on Components.
Scroll down to the subheading - Motherboards, and click on -
4006158R - Intel (Coryville) 945G Motherboard

[ Note* Uses the PCI Express 1.1 technology.
The Intel 945G chip came out May 2005. PCI Express 2.0 technology didn't come out until January 15, 2007.

http://en.wikipedia.org/wiki/List_of_Intel_chipsets#Pentium_4.2FPentium_D.2FPentium_EE_Chipsets

You can still use a graphics card based on the PCI Express 2.0 technology.
PCI Express 2.0 technology is Backward Compatible, with PCI Express 1.1 technology.

You just won't get the full capabilities of the PCI Express 2.0 graphics card.
Will you notice?
No.
Also a Pentium 4 processor is not a high gamer processor. Single Core processor. It is a 'bottleneck' for graphics information, when trying to play intense newer games ]

3) Largest problem/s directly related to a failed computer (About an 80 percent ratio, or higher)

Dirty Computer Inside/Bad Power Supply:

Dirty Computer
A large percentage of computer problems are directly related to the inside of the computer being dirty, as well as the inside of the power supply.
Using a can of air on a regular basis as needed, could have prevented this problem.

(Computer - Unplugged from power.
Open computer case, Touch the metal frame {Non-painted surface} to relieve your body of Static electricity, before beginning to clean)

The hardware components located inside a personal computer, are cooled by air.

Air is drawn in through the front of the computer case, drawn over the cooling components for the Processor, (Heatsink/Fan combo),
and out through an exhaust case fan at the back of the case, and/or, air is drawn out through the Power Supply.

If the finned Heatsink has the spaces between the fins clogged, and the Processor's fan is clogged, the cooling capacity will drop tremendously.

A Processor has a Thermal Limit. It can only get so hot, before it turns off. (BIOS turns it off)
No Processor running, no computer. No computer = No Video Signal on monitor.

Power Supply
When the cooling components for a Power Supply are clogged, (Heatsinks inside, and the fan, are a Power Supply's cooling components), the Power Supply heats up.

Heat = Wasted Energy
The Power Supply tries to keep up with the call for power, and eventually components inside the power supply break down, or fail.

This cause a weak voltage power rail.
1) ALL the lights use less than 1 Watt of power
2) EACH fan uses 2 to 3 Watts
3) A typical Processor uses 51 to 125 Watts at maximum capability. Depends on what Processor it is.

Your power supply could still deliver enough voltage to light lamps, and even spin fans, but not enough for the Processor.

Me?
I would substitute the monitor cable first. Then (Computer unplugged from power), I would open the computer case, and see how dirty it is inside, and the Power Supply.

If you wish to know how to test your Power Supply, simply state so in a Comment. (Believe upper right of page)
You'll need an inexpensive multimeter (About $10 -$12), or a power supply tester.

disconnect signal cable and give power to monitor and see "no signal check the signal cable" massage appears on screen if so then monitor is ok fault lies in cpu open the cpu disconnest the ram and listen whether contineus beep comes or not if comes then ram is faulty if not then motherboard is faulty

take the post(power on self test ) of a monitor connect power cable and disconnect signal cable see that no signal check signal cable massage comes then monitor is ok right cllick on desktop then properties screensaver -power -select -never

Hello there:
This is usually not a good sign
I will give you a couple of things to try out first ok
(1) you may want to try the monitor on a seperate computer to see if it will work if not than the monitor needs to be repaired.
but if the monitor will work on a seperate computer than this just means that your video card on your computer is either loose or it is not working to test this try these steps
you can try to remove the power cord and open the case and remove the power supply cord that goes to the motherboard than press the power button of the computer for 15 seconds and than if you have a reset button press this button for 15 seconds than plug the power supply cord back into the motherboard and try to reboot the machine and see if this will work if not try this
(2) with the computer unplugged remove the video card and clean the gold edge with rubbinbg alcohol and let dry than reinstall than reboot the machine if still nothing than you will have to get a new video card.
*** NOTE*** if your video card is built to the mother board this is a common thing cause they dont last forever so just get a new video card and install and connect the monitor to that one and not the old one ok?
so please try these solutions and you should be all right
best regards michael.

The 280W may not be supportive enough for the computer requirements and is not diverting its power correctly to power the VGA part of the motherboard.