Thanks. I got into safe mode, did some of the checks there. Troubleshooting found no problems and the process suggested trying recovery. I noted the last recovery point was the automatic system update on 3/16. I ran recovery and noticed it went through the first part of the process quickly, but shutting down was very, very slow. Then it hung on restart at the starting windows screen. Makes me wonder if others have had problems since the 3/16 update.
I forced a shutdown and started once again, this time trying 'repair your computer' from the F8 screen. I did get the startup repair screen to open. It bumped along for a while, then asked me if I wanted to use system restore. I said yes again. Then another restart request, and the system would not shut down, again. I forced another shut down and started over at the repair your computer option. Ran Startup Repair from the prompt once again.
This time it ran for a longer time without suggesting a system restore. I am noticing that the dialog box suggested that the system might restart several times during the process--I am hoping this might happen...since it hasn't been able to actually shut down normally at any point so far.
Looking at the repair details, one message failed: System files integrity check and repair, faile, error code = 0x490.
Back to system restore, I scanned for affected programs from the 3/16/11 date and none were found. So I attempted another restart. It would not shut down.
Forced it again. Restarted into Safe Mode, tried to shut down from there. Got to shutdown and it wouldn't finish. Rebooted and couldn't start in safe mode this time. I went to a 3/13 restore point to try again--the 3/16 restore had not worked. It ran the restore, went through to restart, and locked up at the Starting Windows screen.