Windows 10: WIN 10 OEM or RETAIL?

I have a PC today with WIN 7. I will install WIN 10 in it. Can I buy an OEM license and install it on that PC?

:)

 

Upgrading from Windows 10 OEM to full retail. System does not recognize retail version.

I had a machine with an OEM version of Win 10 PRO. I changed the MB and processor which deactivated the OEM Win 10 installation. I purchased Win 10 Full Retail FQC-08788, removed the original partitions from the SSD drive using DISKPART and installed the
retail version. I linked to my existing MS Account and tried to activate the machine, only to be told I couldn't activate the OEM system and suggested I visit the MS store to acquire a valid license.

WHAT GIVES!!! Was it because I linked to my on-line account? Is the old OEM information being held in the UEFI somehow? What do I have to do to get the new Retail version recognized?

 

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??

 

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 ??