If your license hasn't expired...
Login to Angry Alien Software site:
Go to Purchase history... The Purchase history menu option will appear on the top menu after you have logged in.
If you see a UUID listed for the product, deactivate that UUID.
Now open the software, enter your license information (MAKE SURE you do not have any blank spaces before or after the key. This happens a lot when people copy and paste the license key)
After you enter the licensing information, the program will exit. Then you will need to start it again.
If everything goes correctly, the application will start. If not, you will need to open a ticket so we can take a look at your issue.