PC shut off, turned back on once, but never again

[sytrex]

ADM phenom II X4 processor with stock cooler
4gb G.Skill DDR2 memory(2 sticks)
320 Western Digital HD
LG 22x dvd burner
GIGABYTE
GA-MA790X-UD4P mobo
Rocketfish 700W PSU
EVGA 8800GT GPA
COOLER MASTER Centurion 534 case

All the parts are about a month old (except for the 8800GT and the 700W rocketfish PSU which I extracted from my old build) and it has been working fine all along until it shuts off while idling(left it on before I went to bed, woke up and PC was off).

I was able to turn it back on once, the PC worked fine for a week, then shut down again while I was browsing the web. I tried to turn it back on, the lights came on and fan spun for 1~2 seconds then everything shut down again

Then I wasnt able to boot it at all(no power no fan no light)

I tried disconnecting/reconnect each part(including the power cord) still no boot.

Then after couple of tries, I was able to turn it on again... I dont know what did it....

Couple of days later, PC shut off again and now it wont turn on no matter what I did...

I tested the PSU by shorting the 24 pin with paper clip, fan spin for a second then stops(the PSU is not plugged into anything) So I thought it might be the motherboard thats defected

But after I connected the PSU to another PC(the mobo uses 20 pin connector so I used the 24pin>20pin adpator), the light on the mobo came on when i plugged the main connector in, but no power(cant boot, and the light at ethernet port was not on) If the PSU was fine, why wouldnt my second PC boot?

Now I dont know if the problem is the PSU or the mobo?

My other PSU only has 20pin connector so I cannot test it on my mobo..

I would appreciate it if somebody can help me figure out if the source of the problem is the mobo or PSU(or something else) before I buy a replacement.

Dont think its heat problem either, I monitor all the temp when I use my PC

thanks~

Update: I tried to turn on the mobo without the front panel connected as well(short the pins) but nothing happen... so I dont think its power sw problem...

Tomorow I will pull everything out from the case to see if its the case....

 

[apache_lives]

use the 20-pin PSU to test the rig - never seen a 24-pin motherboard NOT work with a 20-pin

also it may be a standby issue nvidia is known for but discharge (unplug system for a few minutes etc) and cmos reset usually cure that

never use generic PSU's

 

[TheDraac]

You say you shorted the 20/24 pin power connector with a paper clip and it only stayed running for a second or two. With the paper clip connected, the PSU should stay running until you remove the clip. If it keeps shutting off, I would say it's bad.

And just to be sure, you are shorting pin 16 the green wire to ground.... right??

Also, pin 8 (Grey) should go from 0 volts (off) to 5 volts (on), that is the Power Good/Power OK status signal that the PSU sends the MB indicating the PSU is generating proper voltages.

 

[sytrex]

Thanks for replies guys

Also I was able to get the PSU to keep running when I shorted it out once when the PSU was outside of the case(with everything plugged in)...Then I was able to turn the PC on again... Then I unplugged the power cord so I can put the PSU back into the case. Now I cant get it to turn back on again... O_O???

I will try the other PSU and let you know what happens. So I can just connect the 20 pin in the motherboard? it only fits 1 way?

 

[sytrex]

Hmmmm turns out, mobo also needs the 8 pin connector which my other PSU does not have (its from a really old pc and it only has the 4 pins...

Should I take a gamble and buy a new PSU? Its cheaper than mobo....

Or do you mean to tell me that the 4 pin works on the 8 pin as well...

 

[jsc]

But after I connected the PSU to another PC(the mobo uses 20 pin connector so I used the 24pin>20pin adpator), the light on the mobo came on when i plugged the main connector in, but no power(cant boot, and the light at ethernet port was not on) If the PSU was fine, why wouldnt my second PC boot?

Assuming two systems have similar power requirements:
If you take a suspected bad PSU and test it in a second working system and the second system no longer boots, that PSU is bad.

 

[sytrex]

UPDATE:

I got myself a new PSU, hooked it up and now my PC is working again!! Yay! So it was the PSU after all...

Thanks for all the help guys!

 

[Pressman]

Ok, Here's an add on new problem:

I had the same issue as described in this thread, with a yes..I know. a gateway.. I'm ashamed of myself. DX4300-03

It would turn off and not come back on , but the Power button light on the tower stayed on, everything else would shutdown, all fans etc and not turn back on without un plugging, power drain then plug back in. It eventually wouldn't boot at all so , since it was 1 month old I let them deal with it, They messed around for a month then gave it back saying , " we replaced the mobo, and it booted 3 times for us." Now an hour into it being "fixed" , it started doing it again. it's totally random , regardless of what I'm doing. It'll run 6 hours no prob. or 30 min.

I just noticed in spec.s that the PS is only 300 watts?!!? Could this be the problem? Seems like with:
ATI® Radeon™ HD 4650 Graphics with 1GB Discrete Video Memory
1TB 7200RPM SATA hard drive
AMD Phenom™ X4 9750 Quad-Core Processor and the usb and tuner cards there's no way that PSU could keep up, but I'm not the expert obviously.