I’m not sure now what i tried for the serial key- i found the actual product key, and it is 25 letters and numbers- the number i first tried, with the 20 numbers, had ‘oem’ as the second set of letters- but my actual product key does have 25 numbers- liek it’s supposed to-
You can also buy Windows 7 cheap at Ebay:
https://www.ebay.com/b/Microsoft-Windows-7-Operating-System-Software/11226/bn_2780793