First, a common problem is Call-Waiting . If you have call-waiting, you will have to disable it so that the beep on the line doesn't disconnect you.
Line noise can cause problems.
If there is a lot of static on your line, this can cause disconnects. Bell Canada may be able to help you. If the line is being shared in the house, make sure that no one is picking up the line, as this will cause your modem to drop. To access this, click the Start button, go to Settings and select Control Panel . Double-click the Modems icon.