Welcome to Beoworld,
nfjoffe: have had it repaired more times than I care to admit.
Your 6000 must have to work hard. First thing to establish, plug another phone in and try a call. Next try the phone (6000) and base at another location, mates house or neighbour"s etc. When you brought your phone to be repaired did you take the base as well ?
Let's know how you get on.