modem not working correctly xp sp2

when i install service pack 2 for windows xp, my modem will not connect to the internet, i cannot add or change any settings(DNS,TCP/other) in any panel (besides they are the same as before the upgrade), i dont get an error message, i can only hear a constant dial tone through the speaker until the operator comes on and says i dialed the line wrong, when i restore to an earlier time before the upgrade i can use the modem…..What is wrong and can i do any thing, i have contacted Microsoft and they refuse to help unless i pay for their service, i am not paying for thier mistakes i am really getting perplexed some one please help