NO DIAL TONE FOUND

WHEN I TRY TO CONNECT TO THE NET I GET A ‘NO DIAL TONE FOUND’ MESSAGE.
I HAVE CHECKED CONNECTIONS, COM PORTS, TEL CODES AND NUMBERS – ALL SEEMS OK.
THERE IS NO ‘!’ OR ‘?’ NEXT TO MODEM IN DEVICE MGR AND IT SAYS THAT THE DEVICE IS WORKING PROPERLY.
HAVE I MISSED SOMETHING?
THANKS.