No one can tell if your license key is cracked or unauthorized.
The most that anyone can tell you is whether your version of Windows is licensed for individual use (vs. use by an organization.)
P.S. The first thing to do when you receive a previously used computer is a clean install, where you erase the hard drive and reinstall all the software. That's the only way to be certain that your computer is free of malware, configuration errors, and setup correctly.