Windows will not shut down

When I choose Start->Shut Down, my computer will not shut down (intermittent problem). It just sits at the Windows ’98 screen, as if it was going to actually shut down. The only way to shut it down then is to manually power the computer off. Is there anything I can do to prevent this unfriendly shutdown? I’ve even tried waiting for hours for the computer to safely shut down, but it just sits there on the shutting down screen. Any help is greatly appreciated.