I think it would be better to get an active hub and use UTP (more reliable and not hackable by the neighbour kid).
As for that TP-Link, I believe it has a hole with a button on the bottom. Try to press that for 10 sec with a needle, that should reset your device to its factory defaults (there should be some LED feedback letting you to know you can release the button).
Hm, is it this?
Isn't that supposed to be connected to your PC? Or if it's really plugged into your router, then check your router first. Maybe it's your router that's out of order and not the wifi dongle?
Forget my first advice, I thought it's something like this
. I don't think wifi dongles has reset buttons (but your router surely has).
Cheers,
bzt