I have one too - I was just messing around with it today, which is how I found your question!
Assuming it really is a re-tuning problem, press Menu on your remote 3 times, which should give you the Auto-tune option. I think you press the arrow keys around the OK button to make it start scanning, and press OK when it has finished.
I was doing individual channels using the second option on the menu (here you need to press the up-down arrows to select the scanning option (a line with a little bar on it) or the channel number you want to attach this tuned-channel to, then press ok).
I hope it is only a re-tuning problem for you!
Pen
Pen Else, April 2005