Welcome to the Community,
what kind of license key do you have? Is it a one for version 5.x?
If you have a license key for a newer version, you may check whether it is possible to downgrade the key in your My VMware portal.
In addition to what has been said, please note that the last version of OSX that Fusion 5.x will run on is OSX Mavericks, also note that Fusion 5.x End Of General Support was on 2014/08/23.
Which by itself was before the release of OSX Yosemite, Fusion 5.x will not run on Yosemite or anything newer.
It goes without saying that such an old OS is woefully insecure and should never be connecting to the internet.
If you want to run Fusion on a recent macOS version then you should get Fusion 10.x (and yes buy a new license)
See the following link for a 30 day trial:
hope this helps,
Wil| Author of Vimalin. The virtual machine Backup app for VMware Desktop Products
| Vimalin : Automated backups for VMware Fusion and VMware Workstation Professional
| More info at https://www.vimalin.com
| Twitter @wilva
| VMware Wiki at http://www.vi-toolkit.com