My computer randomly crashes and restarts its self playing games

[kirby01]

My computer:
Asus A8N-SLI mobo
Nvidia GeForce 6600GT
Athena 450 watt PSU
Maxtor 200GB HDD
AMD athalon 3500+
1 GB (2x 512 for Dual Channel mode) Corsair value select DDR400 RAM
Raidmax Black steel case

it totally crashes and restarts itsself while playing games for about 30 minutes to an hour.
if the game is in window mode it freezez completely and the speaker plays a repetitive noise even Ctrl + Alt + Del doesnt work, i've played all kinds of games the results are the same, i have taken the sidepanel off of my case and put a fan up to it its running on full power, the computer idles at 41, but when i play a game it just skyrockets imediatly to about 56-58 i thought it was overheating, its still a possibility. i just got the CPU fan replaced and i dont remember them aplying any thermal compound at all... the heatsink is usually hot to the touch, it was right after it was overheating, it isnt at the moment tho...

 

[kirby01]

I forgot to mention, the reason i think it is overheating is because after it restarts its self and you would turn it back on, it would just restart itsself again, EVEN in the bios, i have to wait about a minute before i turn it back on, thats why i have decided its not a driver problem, and the game lockign up in window mode might b un-related, im not sure, which is why i decided its probably not a powersuply problem, also this has only happened in games (so its probably only intensive things that would run up the tempurature)

 

[stevty2889]

It actualy sounds more like a power supply than heat. Overheating will usualy cause it to shut down, rather than re-boot. A little more specs on your power supply would help, never heard of that brand. Especialy the 12v rail. You video card will be drawing the most power while gaming..so if your PSU can't handle it..56-58 is rather high for that CPU under load, but not hot enough to shut it down. If they didn't apply any thermal compound however it could be overheating..I would re-seat the heatsink, but clean off any old thermal paste that might be there, and apply a fresh very thin coat.

 

[birdpup]

I agree with stevty2889 above. Here are instructions for applying thermal paste.
Here is information on power supplies.

Also, if the problem is not due to the power supply or overheating, it is important to test the RAM memory with memtest86 or memtest86+.

 

[kirby01]

er it does shut down and not reboot, i didnt mean to say reboot (even tho i did multiple times)

 

[kirby01]

i know im not supposed to bump for a while.. infact im not even sure bump works here... but i really need someones help

 

[birdpup]

Have you removed and reseated the heat sink fan? With the comment that you are not certain of the original heat sink placement, it would seem proper to remove and reseat the heatsink first.

Have you run Memtest?