The same thing happened with mine this morning, I just pressed the button to switch off and then switched back on and it booted in to windows ok.
I suppose you must have tried this?
I`ve never had anything like this happening before, wonderif anyone has any ideas.
There was no disc in cd drive or floppy.
You could try a system restore. Turn pc off; turn back on again and begin to press F8 successively. When menu appears choose safe start and then follow instructions for system restore. This may work, depending on what caused your problem. Good luck.