#6 - July 1, 2010, 8:18 p.m.
If it's a realm-wide issue, i.e., just not a specific character on that realm, I'd first try doing a reset UI.
To do a full reset UI, you will want to save your addons in another spot if you wish to preserve them.
Then rename/delete or move your WTF, Cache and Interface folders while WoW is shutdown. Reboot your system.
Note, if you are running Vista make sure your permissions are set so it does not undo your changes.
More detailed instructions for different operating systems, including Macs are here.
http://us.blizzard.com/support/article.xml?articleId=18761&searchQuery=reset%20UI&pageNumber=1 You could also try rebooting your system/flushing your DNS to reset connectivity to a certain realm, but that's just a tad more complex.
If neither one of those seems to help this situation, tech would likely be the next best step in the trouble-shooting process.