1. Try to connect your computer directly to the ADSL modem bypass the tp-link router. refer to http://www.tp-link.com/en/article/?faqid=152to establish the internet on your computer, and see if you...

Connect the W8968 to one of the LAN port of the WR2543ND. and disable the DHCP server on teh WR2543ND

one more question, the IP address of your computer is in the IP range of the router?

Why did they send your the earlier firmware? you could try to put the router in different place to see if you can get a better internet speed.

If you connect your computer to the printer directly, can you print? you can also try another computer. or post some screenshot of the printer utility with the thread.

Change the channel and adjust the direction of the antenna. I think you could consider a TL-WPA281KIT or range extender or booster to extend the wireless coverage.