Found this good article:
Why Won't My PC Awaken From Power-Saving Mode?
Wake-up woes solved; converting PDFs to Word docs; switching e-mail addresses; recording from a DVD.
Lincoln Spector
Wednesday, December 20, 2006 01:00 AM PST PC WORLD

Windows doesn't awaken from its standby or hibernate modes. What can I do?

Name withheld upon request

Many standby and hibernate problems can be traced to graphics boards and sound cards. A simple driver update might get hibernation working again; browse to Common PC Problems Solved: The Ultimate FAQ for an easy way to handle this chore.

Some applications can cause sleep/wake-up difficulties as well. As a test, put your PC into standby or hibernation when particular programs are running, and when they aren't. If everything works when you're not running a certain program, look for a free update, replace the app if no such update is available, or close the program before you take a break.

A BIOS update could also resolve the matter. Check your system vendor's Web site to see if one is available.

If something doesn't work immediately after your system wakes up, wait a bit and try again. Your computer could take a while to come back. If all else fails, enter the name of the hardware or software you installed most recently along with the words standby or hibernate in a search engine to find Web pages and Usenet discussions on potential problems.