Why would my phone line work but not my DSL?

It had been working fine for years. But one morning I woke up and the DSL was just not doing anything. It's in the same jack and the equipment was all replaced and confirmed to be in working order. When I unplug the phone and run a line from the jack directly to the modem, it doesn't acknowledge that it's plugged in at all. I singed up for AOL and have that going directly to my PC and that is working, but it's seems even slower than dial-up usually is. It's been three months and no one seems to have a clue and I'm getting quite desperate. Any help would be very much appreciated.