I would have to say that it was probably either the cord that you used to connect your modem, or that it was not securely in the modem's jack.
If your modem works elsewhere, and other things work in that location, it almost has to be the one thing that changes, your modem's connection to the line.
But it is possible (however unlikely) that your modem could not detect the dial tone at your friend's house because of the frequency of the dial tone. You can check this by putting an X1 or X3 in the dial string (AT X1 DT) or you can check the box in the phone and modem settings that indicates whether to wait for dial tone. If you dial out and connect without waiting for dial tone, then it is just the frequency of dial tone. This can also happen if the friend has voice mail and gets an interrupted dial tone as a message waiting indicator. Normally the modem will wait well beyond the length of the interrupted dial tone to detect dial tone, but sometimes not. Depends on the manufacturer's defaults.
pansophic