Audi Repair: Audi, a6 audi, head gasket

Question
My 1998 A6 Audi will not start.  I got it checked by a Mech.  He stated low compression.  What can be the problem.  The Mech. does not know.  He is thinging about removing the heads. Any suggestions on what the problem can be.  

Answer
hello
How low is it?? How many cylinders?
Is it timing OK ? I will do leak down test to find out why the compression is low. Leak down test will show leaking valve or bad head gasket.
need more info......................
good luck                           pltech