Return from Sleep/Lock problem

Vista, SP1

I have an issue returning from sleep mode or simply "lock workstation"
mode.

It works fine if I sleep/lock and return within a few minutes.
However, if the system sits for a while, 30 minutes or so, there is a
problem when I sign back on. The desktop appears, but most if not all
icons are blank. Perhaps two or three out of 60 are displayed
properly. They all seem to work, but they are blank. In addition, the
hourglass/busy cursor is displayed and does not go away.

I checked in Process Explorer, and it shows nothing going on aside
form the PE itself and an occasional hit for the mouse and a tiny hit
on DPC. There does not appear to be any other process using any CPU
time. Yet the hourglass is steady.

I can do anything I want on the system (blank icons notwithstanding)
EXCEPT log off or shutdown. I can choose them from the start menu but
there is no reaction from the system.

My WAG is that it is still running the winlogon process and/or that it
never completes - although when I've seen that in the past on other
systems and other versions of windows it was always visible in process
explorer or task manager as an active process taking CPU time.

Ideas?

Please ignore this thread... problem reposted with a different subject
as it has expanded in scope.