Well that sucks. Here are some instructions from the unofficial MyGig website:
Q: My Touch Screen does not seem to function correctly. What can I do?
A: There is a radio option to recalibrate your touch screen. Please press the following three hard keys simultaneously RADIO/MEDIA -> SEEK UP -> NAV (AUDIO on REN). Once you begin to recalibrate the touch screen you must finish. Audio confirmation prompts are provided for each of the three points of calibration, one beep for the first, two for the second and three for the third. The calibration needs to be precise as possible and a PDA stylus would be recommended. The MyGIG radio requires the user to repress each calibration point to confirm the calibration process. A green crosshair indicates proper calibration.
Source - http://mofv.com/mygig/