Printer Works But Fax Does Not

I reinstalled windows 7 home premium 64 bit. Then soon after, my printer checked out ok but the Fax will not work. Its a HP model 4500 printer/Fax. When I do a test fax, it passes all but one test. The error indicates that I am using the wrong phone cord wire and to install the correct one. The correct one is a 2 wire phone cord. I no longer have the original cord. But the install instructions say I can use a 2 wire phone cord adapter to the printer/fax, then I can use a regular 4 wire phone cord after that and then to the phone jack. I tried different scenarios including reinstalling the printer/fax software. Its probably something simple but I speak little computerese.
Has anyone experience this type of problem and how to repair it?

I have found the problem. The printer/fax install instructions does not mention anything about a router. My nephew installed a router (he calls it a router modem) for his wireless. If one were to follow the instructions to the letter, the printer should work as mine did. But the fax would not.
Here is how I made the fix:
I use a dual telephone jack. One phone cord goes directly to a extension phone. The other phone cord goes directly to the EXT 2 connection on the back of the printer. Then I ran the routers phone line which is a 4 wire cord into a 2 wire adapter and then that is connected to Line 1 on the back of the printer/fax.
When I ran another test, I heard a dial tone coming from my machine and I knew I did something right. All the tests for fax passed.