[MtBaldy]

Use an Ethernet cable to plug the computer directly into the DSL modem. Run a speedtest and if you get the advertised speed then the router is the problem. If not it may be the DSL modem or, possibly, the computer.

[Washi]

Use an Ethernet cable to plug the computer directly into the DSL modem. Run a speedtest and if you get the advertised speed then the router is the problem.

That would be the perfect test if his modem and router were two separate boxes. I'm not sure that's the case.