As I know, after upgrade the latest firmware, we have to restore it to factory defaults and reconfigure it. So...hard reset it and you'll be able to login.

Forgot one thing, did you restore it to facotry defaults and try to login its web interface again? I think you should tell TP-LINK people what you have done in details. Otherwise, they may ask you to...

MA180: HSUPA Band 2100 MHz How about your ISP's network?

192.168.1.* refers to a specific IP like 192.168.1.1 or a IP range like 192.168.1.100~199？ “- I then connect a second computer to the WIFI of the router and suddenly the IP of the first computer gets...

Are you changeing it on Interface Setup---LAN page? Is it running in latest firmware?

1. How to find hardware version? http://www.tp-link.com/en/article/?faqid=46 2. How to find firmware version? http://www.tp-link.com/en/article/?faqid=315 3. V1 can only upgrade firmwares for V1; V2...