A7N8X-E Won't Resume After Hibernate

I'm running an A7N8X-E Deluxe with a 3200 processor and a gig of RAM with XP
Pro SP2.

Standby and Hibernate used to work fine.
Now, standby is fine, but if my PC goes into Hibernate AND it's left alone
for an hour or two it will not resume correctly. After the RESUMING bar
finishes, the monitor switches off and I have to press reset and delete the
hibernate file.

If I hibernate and resume within a few minutes it will wake up properly.
I don't know when the change occured, so it's hard to track this problem.
Google searches suggest hibernate issues are often tied to the video driver.
I have removed the driver for my Radeon 9600 a few times using a number of
driver cleaning utilities. No change. I've rolled back one version as
well. Still no change.

Any suggestions would be appreciated.

TIA
Marc