Windows 10: Win 10 upgrade using win 7 OEM key(dell)

My Dell inspiron N5110 did not pass win upgrade compatibility test in back a long ago. now i have changed hardware and want to upgrade to Win10. there are 2 problems I cannot upgrade win10 using OEM product key using either DVD upgrade OR windows 10 download website. How to swap win7 key with win 10 keys?

:)

 

Win 7 OEM to 10 upgrade, will Retail key be allowed

I have a OEM Win 7 Pro system that upgraded to Win 10. Because it's OEM and upgraded to Win 10 I won't be able to move it to a new computer. If I purchase a Win 10 Pro Retail key can I use that key to upgrade the OEM that I
have and move it to a new computer??

 

Does Dell's win 7 oem key works on any win 7 iso version downloaded online?

I have an 8 year old dell PC needs system reinstall. MS don't provide win 7 iso because this PC has oem key so they send you to Dell, saying Dell need to provide system iso. But Dell is no longer supporting win 7 iso. I got error when using dell recovery
toll, trying to create an win 7 iso "no image for this tag".

So, can I download any version of win 7 iso online somewhere and use this key to activate my PC.

 

Win 7 OEM to 10 upgrade, will Retail key be allowed

Last question. My free Win 10 upgrade is less than 30 days old. Can I go back to my original OEM Win 7 Pro?

If so, I found a Win 7 Pro Retail copy for very cheap. Can I then use this to Retail Win 7 Pro to update my OEM Win 7 Pro, move to new machine and afterwards get free win 10 upgrade with my complete system moved ??