Problem with my PC. Please help.

*it powers down

More details please. Hardware specs? Operating system?

yes.
Motherboard: Biostar P4M900-M4
CPU: Intel Pentium 4 3.0 GHz with HT.
Memory: Kingston 2GB DDR2 800
Graphics Card: Nvidia 9600GT.
Sound: Onboard Realtek.
OS: Windows XP SP3.

I've switched the PSU from my PC with that in my brother's, and the system has been running stable for more than 1 week. Any ideas what might be happening with my PSU and my system ?

and the PSU is a cheap one. but it works on the other PC.

What kind is the PSU? Your system could require more power than your brother's. You have a 9600GT, what graphics card does your brother have?

It could be a temp issue. Try removing the side of your case, and blow a box fan towards it. If that helps, your CPU may be overheating and causing it to shut down.

my brother has a 9600GT too. but his 9600GT is not a green edition. and his uses more power. i'll try doing as you suggested and i'll see what happens. thanks for your reply mate.

Let me know how it goes, good luck.

thanks.

Now, my brother's having some problems with his PC. Sometimes when he starts the PC, it freezes on the POST screen. It detects the CPU and shows the CPUID thing under it. To make the system start, he has to reset. We've not been able to locate the problem yet. And the major problem is, the freeze does not occur everytime. We do not see a pattern in the freeze.

Do you have any ideas about what may cause this problem ?

My first thought is power supply. It could also be a bad BIOS, damaged windows install, few other things....but my first thought would be the PSU.

When it freezes, is there a message at the bottom to press F1 to continue?