What's wrong with my DSL?

From this past weekend I’ve been having trouble with my DSL. It will go offline suddenly and turning it on and off doesn’t work. However, one thing does make it come back online. I disconnect the phone line from the modem itself, connect it to a corded phone, with a filter, then reconnect it to the modem and it comes back online. I’ve had the modem almost 4 years. Could it be that the DSL thinks there’s nothing receiving the signal and disconnects? New modem? What else could be the problem?

even unpowered the modem being connected to a live phone line can keep it in a bad state if malfunctioning. disconnect both power and signal for a few minutes to fully reset. plugging a phone in is a good test to see if the line is dead, though it still may not give a good dsl signal. modems can die and last much longer than four years.

I had a lot of problems last week. Could not figure out if it were the content provider, AT&T, modem or router. Unplugged and reconnected everything it has been better this week but not ideal.

Unplugging everything is only a wee bit of a bother but I am curious about how to proceed with a differential diagnosis if it gets bad again.