Source: http://support.steampowered.com/cgi...2VhcmNoX3RleHQ9ZGlzYWJsZWQ*&p_li=&p_topview=1Why is my Steam account disabled?
Check the contact e-mail address for your Steam account to see if Steam Support has contacted you regarding the reason your account was disabled - accounts may be temporarily disabled pending verification of purchase information or account ownership.
We have a zero-tolerance policy for any violations of the Steam Subscriber Agreement and Online Code of Conduct - we will permanently disable all accounts in a user's possession for any of the following activities:
*Piracy or Hacking
This includes using an unauthorized ("hacked") Steam client to access Steam, attempting to register fake CD Keys, or attempting to register a CD Key which has been published on the internet.
*Credit Card Fraud
Any fraudulent credit card use or credit card chargebacks (regardless of when the transaction occurred).
*Hijacking, Sharing, or Trading Accounts
Do not use Steam accounts which you did not create.
*Account "Phishing" and Deliberately Deceptive Activity
This includes contacting other users outside of Steam or over the Friends network under a misleading screen name or e-mail address (i.e. "Steam Admin" or "John@Steampowered.com") and requesting password or account information.
*Buying, Selling, or Trading Accounts
The use and security of your Steam account is primarily your responsibility - accounts which have been bought, sold, or traded will be permanently disabled.
Please see the Steam Subscriber Agreement and Online Code of Conduct if you have any questions about the policies which govern Steam account use and account termination.