Can't Play Minecraft after purchasing?

Can't Play Minecraft after purchasing?

Added (1). I just bought minecraft through paypal, because my bank won't allow transactions to go through Europe. It said that the transaction was complete, but it will only let me play the demo. But it says on the website that they will email me if something went wrong with the transaction, and I have no such email. Am I doing something wrong?

If you just bought it, wait a few days for it to process.