Go to the Network & Sharing Center and reset/check the settings there. Get the correct connection settings from your Internet Provider and set it up again. More info about this in Help.

Thanks a lot for the quick answer! I wish I could've been of help for future "Wan Miniport"-victims - but coming home from work, the problem seems to have solved itself... it works again, and I don't knokw why. I hate computers. ( :