I had this issue and the heater-blower motor and a few other things were out of whack! I replaced the ignition module - wiring, which is a common prob on these cars and it literally fixed all of my issues..including the heads up display issue. Just a little fyi for all of you out there. My sunroof started working again and rear windows, blower motor worked on all 5 settings, as well as the hud dimming issue.
2003 gtp btw, bought it brand new in may of 03 so I know it hasnt been jacked around with other than what ive done. lol