No Carrier detected

After being hit by the Klez virus and clearing it using F-prot, I am now left with 2 machines that appear to work perfectly except when I attempt to access the web. AOL for example, works correctly up to the point of detecting the carrier, It then clears down with the message “no carrier detected”. Changing providers and modems has no effect the carrier is not detected. I have run all the testing equipment at my disposal, including “My PCTools on line” from Ontrack and “PC Check SE” but have been unable to clear the problem. All tests show no problems.
Any suggestions please?