Help please -- Computer wont maintain power on boot

[bd26]

Specs are

AMD Phenom II X4 955
Antec 900 case
GIGABYTE GA-MA790XT-UD4P AM3
CORSAIR XMS3 4gb ddr3
Antec TruePower 750w psu
Radeon HD 4890

Today I was playing a game and my screen went a crazy mix of colors and computer restarted instantly.

When it tried to reboot all the lights and fans went on but it felt like it was pulsing like 0--0--0----------- then repeat. 0's being where the power should be running at. Red small lights were blinking on the gpu/motherboard aswell. Screen stays black whole time.

I reconnected everything and still no go. Removed the gpu and the computer was able to hold power but no way to connect monitor to see. Then I put in this old ati x1400 card and computer seemed to hold power fine but no screen showed on monitor.

So im looking for advice or help to find solution. All I can think of so far is

psu - Cant power things that rely on pci-e connectors? Since old x1400 held power but doesnt take pci-e to psu. (but no idea why screen was black when I put it in)

mb - I tried both video cards in each of the pci-e slots and nothing showed on screen.

gpu - Might just be bad now.. But dont wanna get new card to find out psu cant power it right or screen will stay black when its connected.

Hell for all I know it could be the bios on the board or memory related. Computer runs everthing good otherwise and temps are great.

 

[jsc]

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboarding

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case.

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=youtube_gdata

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.

 

[bd26]

Thanks for quick reply will give this a shot late tonight/tomorrow and post updates if I run into anything new.

 

[bd26]

Well Started to mess with things a little more

Now when I boot the system it no longer pulses with power but 3 red lights get stuck on from the top of the gpu...And the restart button and power button no longer work to shut it off. Everything is still connected right minus the things i dont need. (cd/hd ect)

That would rule out a mb problem right?

From reading 3 red lights mean power or connector problems.

Computer worked flawless for over a year now with only minor trouble.

Next step ill breadboard it, luckly everything is still under warrenty. (though ive heard alot of horror stories about people sending back parts to be fixed or repair)