Same thing happened to my XTL when I first connected it to my pc for using LINE6 Edit. This was years ago, but I remember using these steps I found on one of the XTL forums:
1. Turn off the POD
2. Turn on the POD while holding down the Save and Edit buttons simultaneously
3. The POD's LCD screen should display Init Edit Buffer
4. Push the Output mode button
5. Turn the Select / Select Page knob one click to the right
6. Turn the Effect Tweak / Change Value knob to the left or right adjusting the contrast.
It worked for me just fine. Hope it helps.