If you have Windows 7 with Bitlocker enabled, and are sometimes unable to shutdown your PC properly, check out this article: http://social.answers.microsoft.com/Forums/en-US/GettingReadyforWindows7/thread/66b6e093-9de7-4e76-84cf-322bd1e35f22
The hotfix is available here: http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=975496&kbln=en-us
Symptoms for us were that Windows 7 itself would shut down, but the power would not be switched off from the laptop, leaving it running (often with the fans whizzing away and LEDs on)