Frequent shutdown

Windows me on a Dell dimension 8100 desktop.

Problem is that after an hour (?) of inactivity it will black screen and
will have, on its own, shut down completely. Moving the mouse, space bar or
briefly pressing power on button will not revive it. To restart requires full
reboot.

The monitor does shut off after 10 mins and the screen saver comes on...but
at some later point it goes down completely.

I have looked at the "power options properties - Power schemes tab" and
tried to set it for "never" - no effect.

It really does not seem to have anything to do with sleep, hibernation
modes, as the power button has never had any effect unless I hold it long
enough for a reboot. i.e. its not 'sleeping' its shut down.

I always get an error message when I do reboot and its starts scanning the
C-drive for problems (there is no virus etc)

It would seem like its a setting, but it just started doing this
spontaneously - I never changed anything.

Any idea how keep it on indefinitely or have it go into normal sleep mode -
I just hate rebooting when I come back to the machine afer 1 or 2 hours.