Dell 5100MP - Will not power off.

Greetings,

I have a Dell 5100MP projector.  Intermittently, after a few hours of use, the projector will not respond to any input from the remote or the controls on the machine.  Additionally, disconnecting the source cable does not cause the unit to automatically search for a signal, it remains stuck on the last input (and will still display video from that source).

The issue can be resolved by disconnecting the power from the machine, reconnecting and rebooting.  The issue seems to be becoming more frequent and, given the projector is ceiling mounted, disconnecting the power is by no means a long term solution...

Any suggestions are appreciated.