Soon, however, I heard the access on the Tower "chime", which means that Comcast has reset the modem and high speed service, so it must have detected the problem. Then it all connected.
As it happened, I installed Carbonite backup on my MacBook yesterday as preparation for a music project. (I don't have a Lion OS late enough to use iCloud, and I'm not about to start replacing OS's on a whim.) That resulted in a 10 hour "initial backup" through Xfinity of 9 gig from the MacBook.
During that period, until almost the end, once again I could not sign on to Xfinity through my Dell laptop, although the older XP stayed connected. Is this a matter of bandwidth management? No complaints, because I just used iPad hot spot all day on the Dell (which has to be refreshed if you leave the computer idle and it goes to sleep). Today it all worked as normal.
Picture: OK, I don't dust often enough.