I've had the same problem for like a YEAR!!! XP would lock up Explorer each time I left the computer alone for any length of time, and Explorer.exe could not be killed from the Task Manager. I've tried so many registry hacks and so forth that it wasn't funny any longer - I was ready to format c: and start all over again.

But then last week I just discovered the fix - Simple as pie. I set all power my options to NEVER turn anything off except the monitor (including never letting disk drives and network cards power off), never hibernate, and never go to sleep.

Problem solved!!! It hasn't locked up in days!!! It shows me that Microsoft may be playing some games here, trying to get us to buy Windows 8. Since when should it be hard to make a PC sleep and wake up without locking up??? - GRRRR!!!!