First off, if your account is banned and you've checked off the automatic login box, you'll need to delete your maximumpc.com cookie or you'll keep on logging in with a banned account.
The second thing you should do is find out why you were banned. This is best accomplished by looking at
The Banned List. You'll see an explanation along with the name of the moderator who banned you.
If you think you have good grounds for being unbanned, then you may re-register with a new account and send a Private Message or email to the moderator who banned you and try to work it out with that person. The staff here doesn't undo each others' bans, so you'll have to deal with whoever banned you in the first place. This is easier than it sounds, because with the exception of Alice, we aren't monsters and we'll listen to your side of the story. If you've been banned by Alice, the ban is final... don't waste your time contacting her.
What not to do: Well, a good way to get yourself on the bad side of the moderators is to make a new account and a new thread to whine about it. That will most likely get you banned permanently. We also advise
against calling the moderators names or acting childish.
Hopefully, you'll never do anything to warrant getting banned. But if you do, maybe this post will help you get reinstated.