Computer shuts off

[What???]

Hi, I recently bought a new heat sink to put in my computer. Once I installed everything and hit the power switch it booted up fine but then after ten seconds it would shut off. I thought maybe it was overheating but when I went into the bios the temp said around 44c and then shut off. Then I thought there wasn't enough power so I put everything back the way it was and the same problem occurred. I've tried switching the ram sticks but that didn't change anything. Then I took out the CPU and booted it but the screen read video signal not found. I thought the motherboard bios would come on but it didn't. I took every thing out of the case and hooked up the mobo and the video card with no change. Now it will boot up for a second and shut off with my case still showing its on while my fans have stopped. I took out the mobo battery to. My guess is the motherboard but this is my first build so I was hoping someone elses opinion. The computer is about 3 months old.
AMD xp 2500(not overclocked..yet)
A7N8X-E Deluxe
Geil Value pc3200 512x2
9800 pro
Audigy 2
Maxtor HardDrive

 

[entity512]

I could be overheating. if your bios wasnt updated it will display wrong temps. Well mines was updated and still displays wrong temps in bios!

 

[What???]

Thanks for the reply. Overheating was my first thought but I'm using an slk-900a with a tornado and assumed that it couldn't be it. I guess watercooling is next. lol When I first built it I had this problem. To fix it I took out one of the ram sticks, put it back in, and it booted fine till now. I'm going to try the heat sink again to make sure its not heat.

 

[entity512]

you relize it doesnt matter what cooler you have. You have to seat the heatsink correctly, on the die of the cpu with some thermal paste. And make sure your fans spinning lol.

 

[What???]

Update, I'm an idiot. You where right. I put arctic on my old heatsink and it booted right up. The funny thing is that its now 10c cooler than before. Maybe too much paste. I guess I can't hook up thermaltakes well. Thanks for the help.