agree I would plug all into the router that is much safer anyway since the router will or should have a firewall in it. If it were the ones hooked to the router that had the problem it could be a bad router but if the one you have issues with is not plugged into the router that is what I would try first. One of the first things an ISP tech will tell you is power down your modem and router, disconnect them from all power let set for several minutes then replug and try. Let us know if plugging that one into the router works. You always want to put the router between the pc and the modem to give you the added protection in the router.

Genes, no, I don't use hibernation or sleep or stand by. Let me run this thought through y'all. About the time the computer decided it didn't want to do internet, we had Comcast to come out to check why we got nothing but tiles. While he was here, he took note that we have five TV's and was using several splitters. He unhooked/uninstalled one of the tvs and it got rid of the tiles. Could the splitters have anything to do with this problem? What is such a riddle to me is, why does one computer work on the Ethernet and the other one will not? Hmmmmmm? I've had another AT&T technician back to the house and he found nothing and I took it back to the computer guy and they, again, found nothing. The AT&T guy did suggest hooking up a router and using that. What's the general thought on that idea?

OK so try removing the left side and leave it off for a few days to see if heat is an issue. Is there a build up up crud under the fan you see mounted on the motherboard? This is the heatsink for the processor and it is designed to shut the computer down if it overheats for protection. Remove the power cord if you go in there and rest a bare arm or hand on the metal frame to eliminate static electric. You should seriously consider installing an anti malware program for greater protection. These do not run automatically but you update and run at intervals. Consider MS Essentials, Superantispyware, Malwarebytes or any other program you feel will keep you safe. Those mentioned are all free but pay attention during the install or you'll find yourself installing the 'for a fee' software.

I don't know if you are dealing with cats or dogs. Cats aren't going to stay off, or they will hold a grudge in the process. Dogs, the easiest way would just be persistence with the off command. Middle age they can still learn that. Mine have taken usually a month to really start to learn to break a habit (ie not going in a certain room they were previously allowed in). But, they're still going to try, and still going to do it when you aren't looking. Get a blanket and teach them to lay in the spots that have the blanket. Otherwise the only way to get a dog or cat to stay off would be to give them something more desirable to lay on. I bought a chaise, not meant for them, but they have seemed to think it was for them and go over there now even though they are allowed on this couch.