I agree with that. That "ethernet over power" added a little complexity to the issue. I think you need to isolate the problem. Since the neighbor's laptop wireless connrection is working... take the laptop, disable the wifi on it, plug the RJ45 cord that is used on the desktop to this laptop. Would the Internet connection work on the laptop? If it doesn't, the problem is with the "ethernet over power" set up. If it does, then the problem is with the desktop.
Here's an update based on several things that were suggested. I plugged the laptop directly into the RG with an ethernet cable while the wireless connection on the laptop was disabled. It worked fine. I then took the laptop to the room where the desktop is to test the Plug Link with the laptop. I could not get it to work. Out of curosity I moved the laptop and Plug Link to another room closer to the RG. It worked but it took repeated attempts. I don't know why it made a difference by moving to another room since it is not far from the RG to the desktop. This would lead you to believe that the Plug Link is one possible problem. I then tried a USB wireless card (that AT&T sent) on the desktop. I could not get the wireless card to establish a connection. This makes me think that this is a separate problem. FWIW, the laptop worked on a wireless connection when it was in the same room as the laptop, so interference from something in the room does not appear to be a problem. I downloaded Malwarebytes to a memory stick on the laptop and then loaded it on the desktop. It found Trojan.BHO and removed it. I still could not establish an internet connection with the Plug Link or wireless card after removing this trojan (I did restart the desktop before my these failed internet connection attempts). I'll try running Rkill on the desktop and then run Malwarebytes again. It appears there may be multiple problems or something on the desktop is causing the failure to get a connection on the wired and wireless routes. I may connect the desktop directly to the RG to see if that works. I would appreciate any further suggestions on this problem. TIA.
RE: I plugged the laptop directly into the RG with an ethernet cable while the wireless connection on the laptop was disabled. It worked fine. = = = So this means the RG router is working. It is out of the suspect list. = = = = = RE: I then took the laptop to the room where the desktop is to test the Plug Link with the laptop. I could not get it to work. Out of curosity I moved the laptop and Plug Link to another room closer to the RG. It worked but it took repeated attempts. I don't know why it made a difference by moving to another room since it is not far from the RG to the desktop. = = = The physical distance between the 2 equipment may be misleading. Depends on how the house is wired. His AC power electric cords from all rooms may go only to the main fuse panel. So even if the 2 rooms are right next to each other, the connection may go from room 1 to the fuse panel, then from the fuse panel to room 2. If the plug link thing gets good/bad signals on and off, it can be an issue. = = = = = So all evidences seem to suggest this: - The laptop is working okay, with both wired and wifi - The RG is working okay, with both wired and wifi - The desktop may not be in working condition due to virus (perhaps) - The plug link may not be working right Suggestions: - How does the RG router gets the connection from AT&T? Through the phone line? If so, can the RG be moved to the same room as the desktop? Does it have a phone line outlet? Use the direct wire connection without the plug link from the desktop to the router? - Looks like solving the virus issue on the desktop may be the answer. I assume that this configuration must have worked at the beginning? What is the history of the problem? If it suddenly doesn't work one day... then most likely it is a software setup issue. Using these virus removal apps may not be the answer. In the past I had tried some of those anti-spyware. Turned out they are spyware themselves. Since then I never trust any virus fixing program. Especially the free ones. Bite the bullet, save all data files and re-install the OS and all the apps.
I would drop the word "possible" from that last sentence. As you said Plug Link and wireless are completely separate - you have determined the router works when wired, so now you need to focus on Plug Link and wireless as separate issues. I don't like Plug Link type solutions because they suffer from interference from other things plugged into the same circuits, also as far as I recall if the two Plug Link endpoints are plugged into different wires of type typical US split-phase system they cannot communicate (unless a special device is installed that allows communication across the two wires). Since the plug link worked with the laptop in a closer room but did not work with the laptop in the same room as the desktop then you have determined that plug link in the desktop room no longer works (for whatever reason) so there is no reason to suspect the desktop is the problem when using pluglink to connect in that room - it is clearly the plug link that is the problem in that situation. Yes exactly - that should be your next step.