DiskPastActivate this PC
Install DiskPast, open Settings → License, and paste your key. Spaces and dashes are ignored. The usual shape is DP-XXXX-XXXX-XXXX-XXXX.
Activation uses one seat. Deactivate there or on your account before moving to another PC.
After a successful activate or refresh, you can stay offline for 14 days. Each successful refresh starts that window over.