It seems that you have elimate the possible spyaware. If not, try spybot search and destory or Adware to remove possible spyware.
Have you tried to connect to net use another PC successful on your phone line. If not, there must be a problem with phone line.
If you got the caller ID withhold on your line, most ISPs will not accept the dail up from line. This is just one of security measures most isps used.