Windows 7: Unresponsive

Help please!
Just finished watching a fantastic movie (avi) and the system became unresponsive.
Tried turning off at computer (Windows7) shut down as per, re started and the system went directly to the media centre and was unresponsive. Turned off again, same same..
shut down, turned off and unplugged at wall, re booted and same again...an endless loop of returning to the same media centre screen each time with no change and completely unresponsive to any input from the wireless keyboard (which was working fine earlier to begin the movie etc, and yes checked batteries).
Anyone have any ideas?
Appreciated....

Have you tried booting to the Safe Mode?