First of all, log into any sensitive accounts (e.g. Bank accounts, Online e-mail, Hotmail, PayPal, eBay, iTunes, Instant Messenger, etc.) and change your password incase that information was saved on the stolen computer. Contact your computer manufacturer so they can make a note in their database that the computer has been stolen incase the thief tries calling support. You will need to have the serial number and/or model number of the stolen computer, so that it can be identified.
Mostly, stolen computers can be considered as "Not used further" or damaged completely. I think, that you can download a new copy of Norton 360 3.5 from any of the following links according to the product you have brought(click on the link to to start the download) and activate using the same Product key:
I think you have to handle this as if you had lost your wallet. It's another good reason to have a password on the computer so that no one else can log on except the people who are supposed to log on it. If you have property insurance and insurance on the computer itself, you may even be able to make a claim for the lost computer too. That's something to take up with your insurance company if you have one and if it's covered under those circumstances.