Check that your modem is correctly connected to the computer and the phone line.
If an external or high speed, make sure that the modem is powered up.
If you have high speed, make sure that the rf filter is NOT between the socket and the modem!
If you have dialup, the sound volume during the connection is NOT an indicator of the incoming signal strenght, but is the out bound negotiation signal send by the modem.
Try using another socket closer to the telephone entry. Try to get the whiring as short as possible.
If you have several phones connected, try disconnecting some.
Electro, August 2011