Oh, and perhaps you should just stick 100% to a direct wired connection between PC and router, and disable the PC's wifi completely until we get things working again.
Wifi has a zillion possible issues, and it's best to just remove it entirely from the situation until we sort out basic connectivity.
The only way I can connect at all is to plug the ethernet cable from the PC directly into the cable modem, so wifi is out of the picture.
Attached is a zip file showing every single setup screen the router configuration program has to offer.
I will be away from the computer until about 7pm tonight, I have to take SWMBO into Guadalajara [shudder] for an injection into her damaged knee. About $2100 pesos worth...
Thanks so much for the help!
tanstaafl.