My power switch on gateway desktop, GT5404 does not turn on it only flashes briefly then goes off.

The front of your computer is the Front Panel.

The area of contact pins on the motherboard, that the main wires of the Front Panel go to; is the Front Panel header.

JFP1 is Junction Front Panel 1.
Better method IMHO is to state as Front Panel - Junction 1, so it's easier to understand.

Just some 'trivia' that I thought I would post to you.

Would however like to post;

Anti-Static Precautions

Your body carries Static electricity. Static WILL fry out (Short Circuit), the delicate hardware components inside a computer.
Relieve your body of Static BEFORE reaching inside your computer.

(The Static? More than likely you won't see it, or feel it.
Your computer will,.....POOF! )

Computer ON a table, computer Unplugged from power, computer case open;
TOUCH an unpainted surface of the metal frame of the open computer case.
This action will relieve your body of Static.

IF you leave your computer in the middle of working on it, be SURE to Touch the metal case upon your return.

Since I'm here;

The method to test if the problem is the Power On switch, or the Power Supply; is to use a jumper wire on the 24-pin ATX main power wire's connector,

http://support.gateway.com/s/MOTHERBD/FIC/105552/105552mvr6.shtml

This is an example of a 24-pin ATX main power cable, and it's respective connector on the motherboard,

http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24

A jumper wire is used to BRIEFLY connect the Green wire, to ANY Black wire.
The Green wire is the Soft Power On wire. Abbreviated as PS_ON.

ANY Black wire you see is a Ground wire.
(And that goes for ANYWHERE in the computer)

The preferred jumper wire is a straightened out paperclip.
It is bent into a U-shape. Turn it upside down, and that is how it's used.
The top is wrapped a few times with black plastic electrical tape.
This taped area is for your fingers, and thumb to hold onto.
The 'legs' that come down on each side, are what is used.

One leg slides down, into the back of the ATX main power cable's connector, into the socket hole with the Green wire in it.
[The BACK of the connector is where the wires go in ]

Slides down RIGHT NEXT TO the green insulation of the wire, and goes down in far enough, to touch a female metal terminal.

All wires going into the 24-pin ATX main power cable's connector, end in this style of female metal terminal,

http://www.mcmelectronics.com/product/28-9420&utm_medium=Affiliate&ref=cj&utm_campaign=CommissionJunction&utm_source=CommissionJunction

Looking at the middle photo of the Playtool link, you can barely see the openings of the female metal terminal connectors.
They look like small brass rings.

The other 'leg' of the U-shaped jumper wire, goes down into a socket hole, with ANY Black wire in it.

24-pin ATX main power cable is plugged in, just like the photo to the Right, in the Playtool link.
Power Supply plugged into power.

U-shaped jumper wire is used Briefly. No more than 2 seconds.
(1001..1002)
[The Power On Switch is a Momentary Contact Switch ]

What is the Voltage involved in the Soft Power On circuit?
5 Volts DC.
In comparison two D cell flashlight batteries produce 3 Volts DC.

Just want you to know, so you won't think I could lead you into being Shocked.
Not saying there won't be a small spark, though.
You may wish to wear a glove on the 'jumper wire hand'.

IF the Power Supply comes on, you have a bad Power On switch.
(You noticed before that, but this would have led you right to it)

IF the Power Supply does NOT come on, you have a bad Power Supply.

Going further;
The Power Supply in your computer is an SMPS.
Switched-Mode Power Supply,

http://en.wikipedia.org/wiki/Switched-mode_power_supply

Another widely used term for Power Supply is the abbreviation
PSU. Power Supply Unit.

It converts the dangerous high AC voltage, 100 to 240 Volts, from your home or business; into 3 low DC Voltages.
The dangerous voltage is contained IN the metal case of the Power Supply.

The 3 low DC Voltages are;
A) 3.3 Volts DC
B) 5 Volts DC
C) 12 Volts DC

Gateway Support > Gateway GT5056 Desktop PC > Main Support page,

http://support.gateway.com/s/PC/R/1008835/1008835nv.shtml

In the list click on Components,

http://support.gateway.com/s/PC/R/1008835/1008835cl2.shtml

In the list go to the bold black subheading -> Motherboards
Click on the blue title ->
105552 - Foxconn C51GU01Motherboard

http://support.gateway.com/s/MOTHERBD/FIC/105552/105552nv.shtml

On this page click on -> Product Views

http://support.gateway.com/s/MOTHERBD/FIC/105552/105552tc.shtml

Now you can see where every cable goes on the motherboard.
Let's take -> Q - Front Panel Connector, for an example,

http://support.gateway.com/s/MOTHERBD/FIC/105552/105552mvr18.shtml

Now you can see where every wire goes on the Front Panel header,
JFP1.

I don't know the color code of the twisted wires, that come from the Front Panel.
If -> I had to trace them, I would remove the Front Panel, and trace them to the;
A) Power On switch (PWR SW, or simply SW)
B) Power On LED (Light) (PWR LED)
C) Reset switch, (IF used) (RST SW)
,and,
D) HarDDrive activity LED (Light) (HDD LED)

If I were a betting man, I would bet the Red and White twisted pair of wires went to Pins 6 and 8. Power On switch.

Blue and White twisted pair of wires to the Power On LED. (Light)
Pins 2 and 4.

For additional questions please post in a Comment.
Regards,
joecoolvette

[I know. There's 5 minutes of your life you'll never get back.
I just posted the above, in case you run into this problem someday, and it isn't a loose Front Panel wire ]

use external monitor to setup internal monitor setings

Connect your monitor to a different computer, to confirm that it works at all.

Connect a different monitor to your computer, to confirm that the video-adapter in your desktop is working properly.

Change out power supply with a computer that has worked in the past and has a similar power, supply. Check power supply for 5volts,12volts we are black box specialist noone dors this any more change out power suppy and see if it works

1. your hard drive may be at what is called the "end - of - life"
2. I suggest that you try to backup important files if you can get into the pc screen again.
3. PC freezing is sometimes due to a failing power supply, a failing hard drive, and or a depleted CMOS battery.

With 3 beeps, you are getting a Memory base read/write error, which means your RAM is having a problem.

You can try takng the RAM simm/dimm out and re-seating them back into the slots.

If the issue continues, you will need to replace the bad RAM

Computer has three short beeps as it starts? computer RAM (memory) related issue.

If you've recently added or tried to add additional memory to the computer and have started getting these beeps. Remove all new memory you've added to the computer. If the computer works fine after removing the new memory you're encountering either an incompatibility or defective new memory.

Sometimes when the computer is moved and/or over time a memory stick can become loose causing the computer to be unable to read the memory or get errors as it's reading it. Try fixing this issue by opening the computer removing each of the memory sticks you have in the computer and then placing them back into the computer.

Hope this helps.

The hardware userguide for your computer will show you how to do everything, step by step:
http://support.gateway.com/s/Manuals/Desktops/8512041.pdf

The battery on a desktop computer is on the mother board. It looks like a large watch battery. Very inexpensive and easy to change. But make sure all power is disconnected before touching *********** board and do not use and sharp object to try to pry the battery out.

I have the same model after youlet it sit for a long enough period to cool down it will come back on and work normal, it is a cooling problem called gateway and they confirmed this theproblem I ran in to was what fan this computer has 3. temp fix I used was to remove the tower cover to allow better air flow try this till you can figure out what fan is messing up