I am a new Hummer owner I bought an 06 and just 1 issue has popped up. The indash radio/NAV system when I am in acc. mode I can see the screen make adjustments, use the nav system, etc. However once I turn the vehicle on the screen goes black. Audio still works great. I just can't see the screen until I turn the vehicle off and put it back to acc. mode. Any thoughts? Thanks in advance