Mine did that just yesterday, (I was using the "red button") and a powercycle made no difference.
I got around it by powering on, and keying 001 on the remote, it then went to BBC1. Might take a few attempts.
I have to say my box (ITD58G) has always been quirky and is the 3rd warranty replacement I've had since the original one locked up during a "install update to maintain fonctionality" message (not a typo)
Good Luck!
Rhino, June 2006