If you ever need to reinstall Windows, you might need to enter it. Your product key is important for a few reasons. Every Windows computer has its own unique 25-character product key, and it's formatted like this: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX. Your Windows 10 product key is a special receipt that shows you have an 'activated' copy of Windows. But without a receipt, how do you prove that you actually own Windows?
Windows 10 is installed thousands of times a day on computers both new and old.
