I have added the RAM and SSD to the NUC. When I try to install the Windows 7 (from manufacturer DVD), it will not install saying "Image authorization fail. System can not boot to this device due to security violation ...."
Can you please advise how I can get Windows 7 installed?
Yes, I purchased Windows 7 from Microsoft and received their official DVD for installing Windows 7.
Nevermind: it was a Secure Boot issue I think. I reset the bios to default and tried again and it finally worked.