Try using it. If it doesn't work, call Microsoft or buy a new license. That's basically all you can do.
So I've recently ordered a new custom pc and the parts are on their way. I was hoping that my current OS (Windows 10) on my current PC could transfer to this new one. I have the OS file downloaded onto a USB. If I booted my custom PC up with this USB would I run into any problems? Are OS's tied to only one PC?