Computer turning on and off after swapping psu

[shicity]

Here is the problem. I have an HP Pavillion and I was trying to upgrade the video card. The upgrade required a new power supply.

Replaced:
gt 620 with gt 560ti
400 watt with 550 watt

After all was said and done the computer would not power on. Checked the power supply using http://www.techspot.com/community/topics/tutorial-suspect-a-dead-psu-how-to-be-sure.55506/ method, it works great.

Swapped back to old video card, computer turns off and on intermittently.

Swapped back to original set-up, computer still turns off and on intermittently.

Thought it might be a ram problem. Tried removing each dimm separately had the same issue of turning off an on.

Also unplugged just the 24 pin connector from the mother board, connected ground to ps_on (green) and the hard drive and cpu fan started up fine.

Replaced the thermal paste on the cpu and heat sink... still same problem

Anyone know what the problem might be? I'm guessing (but hoping I'm wrong) that something on the motherboard got short circuited.

 

[ihsaan96]

Well make sure all the wires are actually connected properly and secure. See if any wire has been ripped or pulled out it's connector in the process. If everything seems fine then try your cpu , ram & mobo with someone else's system to see if it is your motherboard. If it still fails then most likely your motherboards been friend during the process :/

Good luck mate !

 

[rolli59]

Start by checking all connection and reseat all slot devices.

 

[mlcaouette]

If the above suggestions haven't fixed your problem, work your way through this troubleshooting list:
http://www.tomshardware.com/forum/261145-31-perform-steps-posting-post-boot-video-problems

Then post back with results

 

[samuelspark]

Could have short circuited your motherboard with static electricity. Just happened to mine with the same symptoms as yours.

Try a motherboard speaker. If it doesn't beep, that means your motherboard is most likely dead.