Can you detect any Wi-Fi using Windows built-in utility instead of TP-LINK utility? Any error message? Did you try to uninstall driver and utility and install driver only? BTW, if there is anti-virus...

In my opinion, TD-W8980 and powerline extender kit should be better. How do you think? http://www.tp-link.com/en/products/details/?categoryid=&model=TL-WPA4220T+KIT

You are not using USB sharing function, right? What kinds of FTP client? Maybe Mac has some application can be used in your case. Try to contact Apple and find some clues.

Are you using latest firmware? What I am interested in is how did you access it using Android? Can you share it? Do I need to install something else? Thank you.

Ross, can you try DMZ on W8980? Maybe something wrong with ports?

Maybe easy setup assistance cannot be running on Win 8.1. It is quite easy to login its web interface if your physical connection is right. You should connect your modem to WAN port(blue) of WR841N...