Computer Restart Problem

I have a problem with the restart function on my Diminsion with XP SP3. When I do a software upgrade, like Microsoft update, that requires a restart, the restart shuts down the computer, then restarts it, but the applications will not start up. It hangs. I then have to manually power off the computer, and manually power it back on and the applications all start up successfully.

Does anyone have any ideas why this is happening ? ?

Thanks - Rice297