Are the powerline LED on? If the lights aren't on, you may need to repair them. If the lights are on, you can check wehther your pc has obtained IP address through powerline units.

How about the powerline LED on the AV600? Are they on? If they are not, you may need to repair them by pressing the pair button.

Very useful sharing~ perhaps you can download the tpPLC utiltiy from other PLC models on tp-link offficial website to have a try. Anyway, you did it.

Have you tried the adatper on another computer? As you said, this is the second adapter you tried but the same issue. In that case, it's recommended to check the settings on this computer itself or...

What's the OS of your computer? Have you tried installing the latest driver? You can also try to change another USB port on the computer.

Even you are near the Linksys E2000, you still meet the same issue? That's to say, you do can connect to extender's wifi but it will lost connection after a while. After you connect to it, can you...