Computer Hanging

Hello,
I have Intel D845PT mother Board and 1GB RAM with 80GB IDE Harddisk. I installed Windows XP SP2 on this. But I am facing following problems.

1. When I restart the Computer It is giving Blank Screen.
2. If Power off the system and Power on the system after 2 to 3 Hours from step 1, It is loading the OS , But After loading It got struck up i.e No input devices are functiioning like mouse,key board.

Can any body give the solution to this problem.

Thanks,
Poorna