my 2007 a6 stereo keeps going off and then on every 3 secs and the cd player is also frozen ...i am really stuck for ideas ?...

 

Sounds like you have a defective component in the MOST ring. This is the fibre optic ring into which the phone, radio, CD player and amp are all looped into. When one of these components electrically fails it causes malfunctions like you are experiencing. The Fibre optics ring would need to be tested with a compatible diagnostic tester to determine which of the components could be faulty.
You haven't had one of these replaced recently have you? Normally they are component protected and have to be released online to function fully, after replacement.