Try going to - Control Panel / Administrative Tools / Computer Management / Event Viewer
Then look at System and Application. System will let you see your shut down processes and should have an error if it is unable to close something that is preventing a full shutdown. Not always, but for me there is usually a clue in the logs.
I have a laptop running Vista Home Premium SP1 [OEM]. The laptop won't shut down, getting stuck on he"logging off" screen, foe 30 muinutes, 2 hours...overnight ! I have to use the power button to force shut down. The next time I tried to boot, the laptop started with the boot menu. In such circumstances, I chosed the obvious - safe mode, which came up with no problems. I then chosed to "check disk". For this, the laptop needed to restart...but then it got stuck on the logging off screen....and this cycles... What do I do next ? Thanks.