Atx12v1 cable when atx12v1 power cable is pluged in the pc will not start up, if the p;ug is disconnected the fan and led works , but monitor does not switch on.pc used to work fine. please help

Hello there, first thing you should do is to check the power cable.You can do that by changing it with PC power supply cable .It is the same. If it turns to be OK then disconnect the VGA cable from monitor and then try to power monitor on.There should be an activity on front power LED. If the power LED is not showing any light at all, then do not go further the unit is not working .Else the power led should blink a couple of times then a window pop up scrolling on the lcd saying :" no video signal" so the unit is OK ..Hope this helps. Cheers.

When you
When you power up your computer and the monitor screen remains dark, the problem can be either be associated with your monitor, or your computer power supply/video card/motherboard or CPU. Perform the following tests to isolate the problem to either the monitor or the computer.
1. Turn off you PC and monitor. Then verify that the 15 pin video data cable connectors are fully inserted into their receptacles on the rear of your PC and on the rear of the monitor and they are tightened down. (on some monitors the data cable is hard-wired to the monitor). Then make sure that both your monitor power cable is securely plugged into a working AC power receptacle. (You can temporarily plug a lamp into your AC power receptacle to make sure you have a good source of AC power).
3. Turn on the power switch on your monitor. The amber colored LED on your monitor should come on. Then turn on your PC. The fans in your PC start to run and continue to run and the LED on your monitor should change from amber to green.
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Now if the monitor led remains amber and the screen stays dark you either have a bad monitor or a problem with your video card, motherboard or processor.. Try using a different monitor. If that doesn't solve the problem, you need to have a PC technician test your computer.
If you have any additional questions contact me by clicking on the "Add a comment" link located under your problem description on FixYa. Also, if you believe that this information was helpful to you, please return to the FixYa website and rate my response to your question.
Best regards,
Yavacotech

Try a different monitor. If the second monitor doesn't work disconnect the power and then re-seat the video card. Also, check the RAMs - make sure they're seated as well. Start-up the computer and verify that the hard drive LED is blinking randomly - if it is, more than likely the computer is working properly. Your monitor could be bad as well as the video card. If the VGA port is on the motherboard, then you have an on board graphics card instead of a video card. In that case, the motherboard is bad.

1) If the monitor has a removable monitor cable, and you have a Known to be good one to use for a test unit, try it. If it isn't removable, try another Known to be good working monitor.

2) If the monitor cable, and the monitor proves to be good, the next thing to suspect would be bad graphics.
Bad Integrated graphics on the motherboard, or if a graphics card is used, a bad graphics card.

3) I suspect it is a bad Power Supply. An issue that comes up so much, that I would skip 1 and 2 above, and check the Power Supply.

A) ALL of the LED lights, mumba_mwaba, use less than 1 Watt of power when in use.

B) EACH fan uses 2 to 3 Watts.

C) A typical Processor can use 51 to 125 Watts. Depends on what Processor it is.
(Older processors such as a Pentium II for example use less)

Enough power to light LED lights, and spin fans, (Or spin a few times and stop), but Not enough power to turn the Processor on.

This is why you may see LED lights lit, and fans spinning, but the computer isn't working.
The computer isn't sending a video signal to the monitor.
No Signal.

Do you have a KNOWN to be good, compatible Power Supply to use for a test unit?
May sound far fetched, but perhaps there is someone who has upgraded to a better computer, and has a computer they're not using, and you could borrow the Power Supply for a test unit.

As you say has become red and no power to the hard disk.
First check the power cable for any loose connections and check if it give power to the cpu and the fan placed on processor starts working as you start the power. If fan it starts and with in few seconds stops then your power supply/SMPS is weak or damage. So replace it for proper working of your computer. And if after power on all fines but red led on monitor and no power to hard disk Try to replace the hard disk power cables because they are not working because of it no operating system is detected and led of monitor is red. After replacing hard disk cables hard disk starts working and still no display or red led on monitor check the vga cable for loose connection or replace it.If you are using vga display from graphic card try to get display first from onboard vga slot.After it your problem will disappear and your pc run smooth and fine.

The red light next to the power button is usuall the hard drive led which should blink every time the hard drive is in use, there is normally a green or yellow light for the power that shoukld stay on constant when the computer is on.

Disconnect all the devices from the computer(tower) including keyboard, mouse, monitor(everything)..even the power cable

Now keep on holding down the power button on the computer tower for 15-30 seconds..

Now release the power button, plug in the power cable, monitor, keyboard, mouse and turn on the computer...

If it works, great!!!

Otherwise, take it for repair..

Starting at the begining. The wall socket, the plug, the cable, the power socket on the SMPS at the back of your PC, the SMPS, the Output connectors from the SMPS to the motherboard. The power LED not glowing means that the power is not reaching the motherboard. Disconnect and reconnect the power connector on the motherboard. start. No start. Does the fan on the SMPS work? If yes then all components before the SMPS are doing fine. If no then most likely connection socket power cable to the SMPS may be the culprit. This has a lot of load on it. The PC and the monitor both take power from this socket. the answer to your problem lies in the answer to my question whether the fan starts in the SMPS or not. If yes then there is no output from the SMPS and the SMPS need to be given the due attention and if no then there is no power input to the SMPS and various cables and socketc need that attention. In case you need to and can remove and open the SMPS look for bulged or burst capacitors. If found, replace them. Those round cylindrical components.

The repeating single beep with a small pause (actually 3 Beeps a Pause) clearly indicates problems with RAM .Replace it ,your problem will be solved . As for connecting the 12 volt 4 pin connector all mobos are designed to sense the presence of this 12 volts and ONLY THEN TURN ON.

Fauza
Hi
First things first:
1) You just change the power on button for other, on Radio Shack they have it.
2) cables that came from the motherboard to the ON/OFF SW. you have to soldering with the new Power Button, thats it. very easy task! you can use any power botton to fix this.
good luck