Thanks... This was the best explanation of my problem... Been trying to solve this problem for months as it slowly got worse and worse. In my situation it was caused not by comcast modem that we replaced, it was a really old wireless router plugged into modem, which was confusing how the modem was processing internet access in windows 7 and vista via it's own internal wifi. Once the old wireless router was removed and everything reset problem solved. So happy with this info on here I signed up for this site! Hope to help other now than ya'll have helped me!