If it is similar to the 2002 TT, then you need to purchase the "keys" to unlock the radio. There should be two small slots on both sides of the unit where you put the keys in. You'll hear and feel a click when it is unlocked, then pull the unit out. Or you can have the radio installation guys at Best Buy do it for about $10. I believe the keys to Audi and VW are the same.
The 2004 Audi TT has 20 valves.
The 2004 Audi TT has an inline 4 engine.
The 2004 Audi TT is a gas-powered vehicle.
The 2004 Audi TT has a 6-speed shiftable automatic.
The 2004 Audi TT has double overhead cam (DOHC).
The height of the 2004 Audi TT is 4 ft. 5 in. (53 in.).
The 2004 Audi TT is 13 ft. 3.1 in. (159.1 in.) long.
The 2004 Audi TT's turning circle is 34.2 ft..
The curb weight of the 2004 Audi TT is 2921 lbs..
The 2004 Audi TT has 48.1 in. of rear shoulder room.
The 2004 Audi TT has 32.6 in. of rear head room.
The 2004 Audi TT has 20.2 in. of rear leg room.