Extremely Weird Startup

Hello, Majorgeeks.

I have an interesting problem.
Computer make is an HP Pavilion Desktop model number a6720y.
Graphics Card is a Nvidia 560 Ti.
I have two PCI-E expansion cards, an unknown brand USB hub, and an unknown brand wireless D-Link Card.
7 Gigs of RAM. 2 1 TB hard drives and a brand new 600W power supply that I just put in yesterday attempting to fix this issue.

The issue is is that the computer turns on, everything goes fine for about three seconds and then turns off. Fans stop, lights turn off, everything, and then it reboots itself. Multiple times, sometimes only 3 times, sometimes 10 times, eventually it gets to the BIOS. I reapplied thermal paste thinking it was overheating, changed nothing, I removed everything except one stick of RAM (which I tested on another computer and it worked fine.) the CPU, the CPU fan, and a monitor plugged in, and it still did it. But eventually the computer does turn on and work fine so I'm having issues believing it's the processor. All fans spin freely, it has been cleaned of dust, I have tried multiple sticks of RAM I knew worked and still nothing. Thanks for any help in advance.

 

Try changing out the BIOS (button cell) battery on the motherboard.

I've had a similar issue on some Intel brand boards and this fixed the problem. If it doesn't, you're only out about $3 for the new battery.

Hope this helps.

 

Replaced it, (had one lying around as my Red Dot sight for airsoft takes the same size cell.) No change.

 

I hate to do this but I really need help with this issue. I have tried everything I can and I can't find a fix. Bump

 

Sorry to say this but it sounds like a motherboard problem to me, make sure you have tested the RAM and the HD first though if you can. When you say you removed everything I presume you included the PCIE cards, also take everything out of the USB's as sometimes these can cause boot failures.