Windows freezing after sitting idle

[IsleOf]

Hi Folks

Im haveing trouble with my PC and i really hope you can help. Ive googled and asked loads of advice baut cant find the answer.

A couple of wweks back my friend gave me his old AMD 3500+ chip heatsink, fan and graphics card. Everything worked on his computer and he was upgrading so theres no reason to believe they are faulty. I bought a new motherboard, new ram and a new hard drive. So basicly ive got a new computer.
I have installed XP and a few small programs that i use. However any time i leave my computer alone for 20-30 mins it hangs. This is with no software running at all. In fact if i leave it during the logon screen it will hang then as well. But i can work away on it for ages and its fine its only if i leave it alone.

Screensaver is off, and so are any power saving otions. The temperature of the cpu has never been above 33°C and fans are working so it isnt overheating

Hope someone can help

[patio]

Have you checked to see if there any power saving options enabled in the BIOS ? ?

[IsleOf]

Yes i checked that. Ill check again though in case i overlooked.

[IsleOf]

Ive checked it and i found the cool,n,quiet feature was on auto. A friend told me this may be the problem if it was on. Ive disabled it now to see if it fixes the problem

[patio]

cool n quiet...COOL !

[IsleOf]

Not so cool. Didnt work. Started my PC with this disabled and left it on while i played some Xbox. Sure enough when in come back and try to do something it freezes.

I really dont want to have to pay for new windows after i fling my PC through them

Any more ideas

[patio]

Just a shot in the dark here seeing how you said you checked all the settings in Power Management...
Go to Start/Run and type in sfc /scannow and hit Enter...have your XP CD handy as it will ask for it.

p.s. Did you remember to use thermal compound when you installed the CPU ? ?

[IsleOf]

Yes power management is set so it never manages power. i.e everything is always on.

Thermal grease was on when CPU was installed. temperatures seem fine.

I cant get sfc/scannow to run. 

[IsleOf]

Sorry. When i run sfc / scannow a dos window pops up then disappears again. Too fast for me to read. I must have blinked the first time and missed it