Not quite sure about the problem. Maybe you can try to use the latest firmware and see. http://uk.tp-link.com/support/download/?model=TL-WDR4300&version=V1#tbl_j

You can set a username and password for the USB hard driver. Here is a link on how to do that: http://www.tp-link.com/en/article/?faqid=254

Go to this website and download the latest USB printer controller. http://www.tp-link.com/en/support/download/?model=TL-WDR4300&version=V1#tbl_j Or upgrade the firmware of TL-WDR4300 to the latest...

Other brand power line adapters or TP-LINK? The Nano adapter you listed can be compatible with AV200, AV500 and also WIFI extender from TP-LINK.

I do not think the distance is the problem because on the TP-LINK website it says it can transfer over 300meter http://www.tp-link.com/en/products/details/?categoryid=&model=TL-PA251KIT. It should be...

The middle light indicates the communication between the two units. You can try to reset the unit to see if they can establish the communication again. http://www.tp-link.com.au/article/?faqid=321