Why would 1 of my phone jacks cause my other phone jacks not to work?

Question

I have 3 phone jacks in my house. 1 which is a double jack, which I wired in myself. After the wires leave the jackbox outside my house, i put a splitter in. when i test every jack, my tester claims its all wired correctly. but when i hook my fax machine up to the newly installed double jack, it makes the other 2 jacks act like a NO LINE. and the second double jack which my DSL modem is connected, dissconnect when the fax machine is in use.

Answer 1

Sounds like the fax machine is causing a problem. Can you move the fax to another jack and see if everything works?
I had a problem once, where I had to put a 50 foot telephone wire in one jack and run it along the floor to another room to get everything to work. Don't know why, but that fixed it.

Answer 2

It sounds like the fax is the problem. Do you have the cord in the correct jack on the fax? Some have an answering machine out. If you are plugged in to this, it could give you an "off hook".