Sleep mode

When I first purchased my laptop, the machine would go
into sleep mode after a few minutes. This really
conserved my battery. When I changed batteries, the
option doesn't seem available. Is this an XP option or a
pc (Compaq) option and how do I reactivate it?

I just installed service pack 1 update on my XP machine
and had no problems with install. However, now when my
computer goes to screen saver mode, I cannot see desktop
or do anything after waking up computer. I just have a
blank screen with cursor. CTR-ALT-DEL won't even work.
I have to do a hard reboot. Should I restore to previous
date and try reinstall service pak 1.
thanks
Perry