Vince: Has it alway done this or did it just start? Did it start doing this after downloading something?
If you downloaded a program which has caused the problem, try uninstalling the program - there is a utility under Control Panel that does this for you.
You could also try going back to a Restore Point.
Does your computer have an image of the operating system on drive D - frequrently the hard drive will be devided and an image of the operating system will be available.
If all else fails there are third party utilities that will shut down a computer. The following is one is freeware: www.slawdog.com. There are additional programs available at Komando.com - click on Downloads.
Tomsys