This kind of issue that happened to you is really weired. The connection should reset it's default values every time when start up/ reboot that is what I experienced with my ISP an ADSL wired connection, despite sometimes I lost connection but it lasts quickly or longest time was around 20 hours not more than. The only thing I need to do is restarting PC and Modem, voilà it works again so in short message this is a very strange case and I hope you will get help very soon. Happy Computing.
Best Regards.
whisper