Automatically restarts when i download

[SECUR1TY]

im new so i didnt know where to post, i hope here is alright.

when i download anything from anywhere, be it from a web site or a download program, my system restarts. i've just formatted my computer and it still does it so im thinking its a hardware problem. but what?

i've got a p4 2.8ghz running on windows xp pro
gigabyte hard drive
seagate hdd
1024 ram
500w power supply

i hope that helps.

thanks guys, any help will be appreciated.

[SECUR1TY]

and i've just noticed it does it when i go into msconfig too.. so now im starting to think its a virus.

[GX1_Man]

Have a read:

http://www.computerhope.com/cgi-bin/yabb/YaBB.cgi?num=1144733358

What happened prior to this? WHat previous problems?

[SECUR1TY]

my system was fine prior to this happening.
i tried a disk defrag to speed up my system a while ago and it happened after that i think. im not sure if they were related, its just all i can remember happening.

i cant download anything to help because it just restarts after 1sec of downloading!

what do i do?

[GX1_Man]

Download from another computer and burn to disc. If you are lucky you will be able to load the programs. Let us know.  

[SECUR1TY]

i tried ad-aware and RegCleaner which i had backed up already.. as soon as i run RegCleaner it restarts.
im thinking its a really bad virus.. but how is that possible after a full format?

[GX1_Man]

I think it's bad hardware. Windows, even a fresh reinstall, will not fix that!  

[SECUR1TY]

but it was working fine before, then it started playing up 2yrs after the original install.
and just now after the format.