Winxp Keeps Restarting....help

[SLIPKNOT]

My PC has just gone beserk. It just keep restarting itself as if someone just pulledout the plug. Sometimes it freezes on the Intel Inside screen. sometimes it loads to WinXP screen and gives me the Boot Options screen. I tried Last Good Configuration. Does not work. Sometimes it gives the following messege:
Windows couldnot start because following file is missing or corrupt.
\windows\system32\config\system
I tried a repair installation. couldnot do it because it restarts in the middle of the process.
I managed to boot in safe mode & cleared all start up programes. In System Startup & Recovery I cleared the Automatically restart dialogue box. Problem continues.
AND this takes the cake: Sometimes when I am lucky ...It boots normally and works... atleast for 20-30minutes...Dont know what is happening. Help me please...
I have a P4 3.6 GHz machine.
OS- WINXP Pro SP2;
HDD- 2, 20GB & 40 GB (Segate and Samsung)
[1st one old & makes noise.. if that helps..]

[Hackattack]

Please use normal font. Thanks.

Now for your problem , 3.6ghz whoah now that processor was known for overheating issues. So my first guess is your proccy heatsink paste has dried up which is making it like a frying pan, if u getting what i mean .

So you can start by cleaning your proccy and apply some good quality thermal paste.

[SLIPKNOT]

Thats all..? Lemme see.... Thanks for the reply dude!

[Sinja]

yep xp acting up like that is most of the times a heating problem even i had the same problem. got a new fan fixed n did some cleaning it works jus fine afta dat

[praka123]

^check ur bios for acpi options.swap between ON or OFF to see which option fixes the restart issue

[wizrulz]

it can be case of ur hdd partion on which xp is installed going bad....install OS on diff partition....from good XP cd

[pramodv1988]

Does the PC restart in safe mode too? If yes then maybe your mobo is corrupted. Might be a hardware problem.

"I tried a repair installation. couldnot do it because it restarts in the middle of the process."

According to this I feel it wouldn't be a software problem. For overheating I believe a error message comes sayint the last system shutdown was due to thermal overheating.Correct me if I am wrong.