Did you uninstall avast from the old desktop first before shutting it down? Avast would know you did that if you were connected to the internet when you did so, and thus free up that license for use on your new system.
We're assuming you've single-use licenses for both the laptop and the old desktop, hence the need to free up the single-use license currently in use in the old desktop so you can use it in the new one.
The old desktop should have the license number recorded in Menu>Settings>My licenses, if you did not uninstall already.
That knowledge will help you determine what license is which for what system. You can also get a current copy of that license provided you've already registered at
https://my.avast.com/ using the email address you used to register your licenses with. You can also have avast resend your license if you don't have a copy on hand:
https://www.avast.com/resend-license-paid.phpTo reiterate:
- Record license information on the old system.
- Find and get the correct license before proceeding.
- Uninstall avast from the old system while online.
- Install avast and insert the correct license while online in the new system.
Hope this helps.