Hi,
I have very confusing problem happening for last 2-3 days.
I am using P4 2.66 Ghz,915GL intel original mother board,256 mb ram and win xp.
My computer hangs after few miniutes(2-3) of operartion. When when I press restart button the whole monister sreen goes blank(grey colour). The I will have to turn of my power. Then when I restart it both smps fan and cpu fan works but no signal come to monitor ar keyboard but power LED and hard-disk LED is on in a constant manner. After waiting for 2-3 hours when I again restart it starts booting and again hangs within few miniutes and then simlar type of situation happens.
I am using 400watt smps. Is it smps problem or motherboard problem? I have no clue.Please guide me.
Thanks
Sourav

Do you have another PSU you can try? It might also be overheating; either the case itself or just the CPU. You might want to look at the temps of your system because it sound more like a heat problem than a power supply.

What is the psu? is it 450watt or 400 watt is good?

PSU is Power Supply Unit. The wattage doesn't really matter as long as it can handle your needs. Just add up the wattage of your components (if known) and add an extra 15% or so for safety. Just remember that the higher the wattage, the more it will cost you to run.

Definitely sounds like a hard lock from overheating. Either your processor is getting too hot or perhaps your video card? If you're not too technically savvy I would be hardpressed to tell you how to check the fans/heatsink/thermal solution on them. You may be better off paying for support at a local computer store IF you can't figure it out on your own.