Select your modem from the list and click the Properties button. Next, select the Connection tab at the top, click on the Advanced button. Make sure that you have all the check marks set as indicated on the picture below. Insert your init string in the Extra Settings field. Bring it up and click on Config to get to the screen with the modem init string on it.
Line noise is perhaps the biggest single reason for dropped lines.
Understand that the local phone company doesn't guarantee that the normal voice lines running to and from your house will be suitable for modem use. The lines they give you are supposed to be able to pass most sounds in the 300Hz to 3000Hz range. Normally, there is no more than a -10db loss of signal from the local telephone office to your standard jack. Most users connect at these rates every day. There are several conditions that can degrade the signal quality on standard phone lines.