I have had a F90BT installed in my car for about two months and has worked like a charm! I just installed a 12 inch mtx 8500 square subwoofer with a MTX thunder elite 801D amplifier. We have everything installed and the system works. But after three minutes the screen shuts off. After the Boot up process. This happens with radio, ipod, cd, and no music at all. Please help me!

Sounds to me like it might be a voltage issue, Try turning the volume completely down and see how long the unit stays on. if given watts(800) and volts(12) then you can calculate amp draw with watts/volts=amps, therefor 800/12=66.666 amps. you might need a second battery or better yet a better alternator to handle that much power. if you let me know what car you drive i can find out how much power the alternator puts out.

EDIT: i see from your name you prob drive an RX8

the stock alternator in that car (i am guessing an 06 but the should be the same across the whole lot) is only 100 Amps, so even if you are at half vol you are using 33 amps just to drive that single sub(not to mention the Avic and the rest of the car)

but before we get to that try turning the vol all the way down and see what you get.

let me know, goodluck.