Okay,
1.Check the phone line for constant dial tone (clear any 1571 / call minder messages if you get the intermittent dial tone),and make sure the line isn`t noisy or crackling as this can cause problems.
2.Check all wires are connected from the phone point to back of the PC-Remove any adaptors that may be plugged in as they can cause problems.
3.Ask him to click on the Internet explorer icon and prompt the pc to dial out,when doing this ask him to make sure his logon details are there (username,password and dial up number)
4.Ask him to try to connect,and write down any error messages that may show up if problems persist.