In general, TMG7 should run fine under Windows 10. The PDF driver won't work. And there won't be word processor output under 64-bit Windows but that was a limitation long before Win10.
You need to unlock TMG two ways...
1) Unlock while running normally as a Standard user.
2) Unlock while running as Administrator. Right-click on the TMG shortcut and select ‘Run as administrator’. Respond to the prompt affirmatively and then unlock TMG. After unlocking, exit TMG.
Unlocking as administrator became necessary beginning with Windows 8 when the operating system began periodically removing the TMG registration information. Windows 10 made another change requiring unlocking by both methods.
You can get a license for TMG9. It will also run fine under Windows 10 and, again, the PDF driver won't work. And you will have word processor output under 64-bit Windows versions. Check this topic for how to buy a TMG9 license.