I just finished building a new computer with parts given to me by my friends Jon and Max. The thing works great, but I've got Wi-Fi issues.
I bought this wifi card. It worked fine, but for some reason the signal strength behind my computer was terrible (two bars or so). This was bad.
Using my cell phone, I noticed that the signal strength was much higher a few feet above the back of the tower, so I bought this USB wifi adapter, which I could place several feet away.
This initially worked perfectly. The computer is a dual boot—Windows 8 and Ubuntu 14.04—and it worked in both. Then, a few days later, it stopped working in Ubuntu. It would disconnect and reconnect every few minutes. This change coincided with my accidentally plugging a cable into my shitty USB hub backward, shorting out all the peripherals and causing the wifi adapter to shut off and reconnect. I can't be sure they're related, but I can't think of anything else that changed.
I found this thread on the subject. Apparently, I have the TL-W822N V3. Versions 2 and 1 worked fine with Ubuntu, but Version 3 doesn't. This doesn't completely fit, since it was working at one point, but I couldn't find anything else to try.
I ran the code at the top of Pilot6's answer, and rebooted.
Aaand found just a blank white screen that didn't respond to any input. I should mention that also coincided with installing Dropbox, so that may have caused the problem. Not sure. Anyway, I tried a few things, but this was a new install anyway, so I figured I'd just reinstall Ubuntu.
My new install had the same problem. I tried the second suggestion in Pilot6's answer.
I tried the solution suggested in Rajat Pandita's answer. Also didn't help.
Finally I tried the solution in Pilot6's second answer.
And it worked! So, there you have it. If you're having this issue, maybe this'll be useful.