The Ringer Equivalence Number (REN) limit dictates how many telephone devices you can connect to a telephone line (you have one line for each telephone number in your house, most homes normally just have one), in most cases the REN limit in your home will be around 4 devices, with your modem typically counting as 1 or 1.5.
In English this means that if you count how many telephones, answering machines, fax machines and modems are connected in your home the number must not exceed 4, if you have any queries regarding this subject you should contact who ever provides your Telephone Line (BT, Cable & Wireless etc.)
Exceeding this limit will usually prevent your telephones from ringing when calls are coming in, and affect the general reliability of all telephone devices plugged in to that line.
Is your modem connected and powered correctly?
1. If the modem is built into your computer (known as an 'internal modem')
check 1: ensure that the telephone line is plugged in to the rear of the modem in your computer, and the telephone wall socket. (To identify the modem look for a connector on the back of your computer similar to the one below)
If the modem is not built in to your computer (known as an 'external modem')
check 1: ensure the telephone cable is plugged in to the telephone socket and the rear of the modem.
check 2: ensure the modem power cable is connected and plugged in at the wall socket.
check 3: ensure the data lead is plugged into the port on the back of the modem and the computer.