To find out the firmware version, you may have to reset it to factory defaults first. Waiting for the screenshot... :D

Can you still find the Wi-Fi name on the phone? Reset the router to factory defaults and have a try.

Remember to update progress of this issue if possible. :) Appreciate it.

You are suggested to consult differences between V1 and V2 here. http://ticket.tp-link.com/index.php?/Tickets/Submit

Link Aggregation? What have you done? Did you bind two network cards on your PC?

Using the same PC, connect directly to your modem and test if you can download properly. Disable ESET and test. When browsing webpages by the router, there is no problem at all? Try to upgrade the...