My PC's Always reboot after several minutes on

Hi,

i dunt know why, but my PC's always reboot after it logon for several minutes... ( about 15 minutes from it on maybe)
my PC's spec :
P IV 2,4 Ghz
512 RAM
GForce 4 64 Mb
Asus p4VPMX
1 DVD Room
1 CD Rewrite
1 HDD
OS Win Xp sp2
SCard Sound Blaster
Also Scard n VGA on board (i've disabled it from BIOS setting)

is there a trouble with my PSU? ( 450 watt)?? or anything else...
FYI, i've reinstalled the OS once n the problem still the same,
please help me...THX...A BUNCh...

 

Is your system over-heating? Have you run a memtest?

 

yes, im dunt try memtest yet...
i think it's not over heated... cuz from the bios info bout my PC's voltage ( vcore, n cooler etc).. it seems to normaly.. n it happen just when i turn the PC's on not over than 15 minutes..:confused n i didnt run any programs ...
sumtimes it's hang...
or reboot automatically...
i've check the processor temp, but it still cold...
after restart several times ( 3 - 7 times), the CPU runs normally, but it never took so long... then reboot again..

 

Right click my computer>properties>advanced>startup and recovery>and uncheck automaticaly restart.If something is wrong then you will get BSOD,and you can see what is wrong with your computer.Post what you get.

And WELCOME TO MJ!!!!!!