my computer was stolen

If you have more than one computer authorised (if you don't then can you authorise a computer ?) then you can log into your account on a computer's iTunes via the Store > View Account menu option and 'deauthorise all' (which you can do once every 12 months) and you can then authorise/reauthorise the computers that you still have : authorising and deauthorising.

Hey, you can open iTunes Store and click on 'Store' in the menu (Ctrl+B if you don't have the menu bar). Then click 'Check my account (your apple ID)...'. This way you can desauthorize all computers and reauthorize the ones you want.😉