Ok, try re-installing it again but do a registry clean beforehand.
If still nothing, it sounds like the clean up removed some parts of your system files which communicate with your pc and modem.
To eliminate any hardware or driver problems, under Network Connections, right click your dial up connection (should be the one saying your ISP provider with the words "connected"), click properties.
Click on the "Configure" button and check the device is working properly and on the Resources tab, check there are no conflicts.
Have a read of these websites and see if you can come up with anything good:http://support.micro...kb;EN-US;163391