First, check the Service Alerts to make sure your server is online.

It can take some time before your character is completely removed from the server after a crash. Try logging in with a different character, then log out and back in with your original character. You may need to wait 15-20 minutes for your character's data to clear. 

If you are still unable to log in, disable all addons that you are currently using to see if they are creating the issue. You can enable these after you resolve the issue.