CPU shutdowns without prompt

[faztp12]

Hi guyz,
Im facing a lil prob here..
The cpu turns off simply, and after a sec or two it restarts again.

Switching ON the CPU at first takes me till the boot.
Later it takes me till somewhere before the first try.
And after a couple of restarts, I wont b able to see the BIOS startup screen itself. Keeps restarting even before that.

All this could mean I have got a bad heat sink.. ryt ?
Havent changed it yet. But waiting for what you guyz think the reason could be

Thanks in advance

 

[cemerian]

is it a new build or a old pc that just started acting up, what are the system specs, is the cpu overlcocked,any new drivers recently?

 

[faztp12]

its an old PC, like 2years, running i5-2400.
Nop no overclocking, nothing just it wasnt used much..it was rarely turned on..