I can't login or change resolution

Hello. I recently downloaded the lich king expansion from here and I'm having the following problems:
Firstly, I can't log in with my account here, the message I get when I type in my credentials is "The information you entered is not valid.", while it is, indeed, valid (doublechecked it).
Secondly, I can't seem to change the resolution. When I try changing the resolution to 1920x1080 (which is my screen's resolution) the game basically minimizes and changes absolutely nothing. I have tried restarting it over and over again, yet nothing changes.
Thanks in advance for the support.

be sure your password is less than 15 characters