I'm not entirely certain what you mean
which operating system
how much memory (right click my computer | properties)
what service pack, how much RAM)
how big hard disk - how much free space
crashing to screensaver?
by default if the mouse doesn't move windows will lock your machine with the screensaver
if no password - the ouse should wake it up
if password - password wakes it
I've seen a few machines where the power management takes over and the machine won't wake up
follow this
http://www.microsoft.com/windowsxp/using/setup /learnmore/russel_02march25.mspx
disable all settings - that way the machine should stay awake - see how (if) that works