There are a couple of reasons why your Snapchat account might have been disabled:
- You have broken their terms and confditions of use
- Your account has been hacked and they have disabled it to stop the hacker doing anything bad with your account (like sending your friends nude selfies).
- You received an email about resetting your password which you ignored/didn't see. Sometimes they take this to mean your account has been hacked and suspend the account.
What should you do if your Snapchat is disabled? What I did was contact the Twitter account on https://twitter.com/snapchat
There's also a support contact on the site: support.snapchat.com/