Re: DSL Connection Speed
The fact that it worked for a matter of hours makes it unlikely that the wiring would suddenly go bad... unless it's been rainy and you've got water in the connection somewhere or if something like a yanked cable or a staple damaged a cable or connection. If you can rule those out, I think you're right to be suspicious.
Can you plug the modem into your outdoor box, connect it to the computer with a long ethernet cable and bypass the house wiring for a test? That would help you isolate whether the house wiring is at fault.