Car Radio No Sound at Startup? Troubleshooting

My car radio with the CD changer in the trunk works perfectly as long as the radio is turned off when the engine is started. If I leave the radio on when starting the engine, it sometimes works, but usually only the display turns on, and no stations are displayed. There's also no sound coming from the speakers. This seems to interfere with the radio's operation to the point that even turning the engine off and on again with the radio turned off doesn't always fix the problem.
Whenever the radio is turned off using the ignition key, the display shows 'TIM 2H'. What could be the reason for this?

A6, year 2001, with a small navigation system and a 6-disc CD changer.