Win XP stand-by not working

Hope someone can solve this for me.
Until a few day ago I would put the computer into stand-by and all was well. I then installed two programs, a demo of Home Theatre by Intervideo & Logitech mouse driver/program. This causes the computer to go into stand-by as usual, but the fans do not turn off as they used to.
I have removed both programs with no difference.
Also as a side issue I can not restore to an earlier time as only two restore points are avalible, both after the problem. Any help on the restore issue would also be very helpful.

Your computer is probably going into suspended mode, and not hibertanation.

Power management can be tricky. Almost all power management issues can be directly related to a hardware driver. Check the “mouse driver” and make sure that you have the correct driver for your particular mouse. Go to the manufacturers web site and get the most current driver. Also, read the release notes for any issues with suspend mode. You can also install a generic Microsoft mouse driver to see if it supports “suspend” mode.

Might not be it, but is ACPI enabled under power management proprieties ?

You got it, may bios settings had been changed.
With programs would list all changes, make tracking this sort of annoying problem down much easier.
Thanks to both of you for all the advice.