Testing a phone cable length
Testing the wiring is an interesting project in and of itself, but there may be a simpler and more effective way to address the overall system, at least before resorting to that:  Can you take the DSL modem and a laptop to the service entry point and try it right there, thus eliminating the wiring issue?  If it works there, then you work on testing your wiring; if it doesn't the problem would seem to be either with the carrier/drop or with the modem itself.