The most obvious cause is that you've neglected to plug your telephone line into your modem. Double check to make sure. A common problem is plugging your telephone line into the wrong jack on your modem.
Many modems have two jacks, one for the telephone line and one for a telephone handset.
Double check to make sure. Double check to make sure that all other devices are on-hook. There may be a problem on your telephone line. These unexpected sounds can make the modem think there is no dial tone. Using your mouse Right click on the dbTechnology icon and in the reulting menu select 'properties'.