I've never heard of an ADSL only line, so you should expect a dial tone. If you don't get a dial tone the socket is dead.
First, unplug everything from the phone line.
Trace the wire leading to the socket back to where the line enters the house. Find the first socket (there may only be one).
Unscrew the front of the socket, there may be another socket inside. If there is, remove the front plate and try the secret socket inside (this is your master socket).
Try equipment that are known to be working (filter, cable and modem). If you have a spare set of equipment try them too.
Once you've done all this phone the ISP and say that you have a problem with the line, you're not getting a dialtone and you have tried a known to be working modem and filter on the mastersocket with no other devices plugged in to the line. You should get a decent response then.
In my experience your ISP will run a line check which will report no faults, it'll get passed to BT wholesale and it'll start working in a couple of days. You most likely won't hear back from the ISP. You almost certainly won't hear from BT Wholesale.
Edit: I've presumed you're in England. If not I suspect you'll need to do exactly the same but replace BT Wholesale with whoever owns the lines, or if you're in England and LLU'd it'll be the ISP's own equipment so you should get a better response.