My son's laptop came with Win 7 Home and was upgraded to Win 10.  Years of great service.  This year, he started to bog down so he tried a system restore to factory defaults. As the laptop comes up, it asks for keyboard and language settings, he hit "next" and it says "please wait" as it continues installation. After a couple minutes,  it then repeatedly boot cycles and repeats the keyboard/language process over again. 

We went to the Dell website to download a recovery disk and it claims the service tag does not exist. Microsoft sends me back to the Dell website to get the software. The CD key on the laptop is for Windows 7.  How do we restore the laptop back to Windows 10 without a recognized service tag, media, or Win 10 CD key?