This post provides step-by-step guide to help you activate Windows 10 by using CMD. Step 1. You can press Windows + R key on the keyboard to open Windows Run box. Type cmd, and press Ctrl + Shift + Enter to open and run Windows Command Prompt as administrator. Step 2. After you enter into Windows 10 Command Prompt, you can copy and paste this command line: slmgr.vbs /upk, in the Command Prompt window. Hit Enter to execute the command. Step 3. Next you can copy and paste this command line and hit Enter to install the Windows 10 product key: slmgr /ipk NPPR9-FWDCX-D2C8J-H872K-2YT43. Step 4. Then you can type slmgr /skms zh.us.to command line and hit Enter Step 5. At last, copy and paste slmgr /ato and hit Enter to activate Windows 10 for free with CMD.