When your account is disabled OR you're just not allowed to be logged in. Here are some solutions to solve it, I've been through this situation for a number of times but has successfully got my account back.
Go to 'Sign Up'
By that I mean, go to the button that says 'sign up' and fill in all of the blanks (such as username and password). If you forgot your password, press the 'Forgot your password?'.
It's always important to remember your username and password because they are what enables you to create your account. It's also better to keep your account, than create another alternative ones.
What if Doesn't Work?
Just wait for a moment and then try again. It worked for me, so it'll definitely work for you.
Staff are the people who work for the wiki, so basically they are the ones who knows how to solve everything (in the wiki of course).
It must be noted that any problems must be sent to Staff by using a Special:Contact. Though, the staff most likely won't respond instantly after you sent them your email, due to staff being very busy individuals themselves too and you should respect that.
The bestest way is just to wait for staff to respond. Remember, every email you sent them MUST be valid, because sending them random emails would actually waste their time.
Reason Why I Made This Blog
Many users seemed to have suffered from this situation, including myself so it's best to make a blog post of how to help solve this problem.
You can contact me on my message wall (this link doesn't send you to my message wall, but my profile instead).