AVICinRX8

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!