I have installed Win 7 Full with no product key. Will I be able to activate it with a valid unused upgrade key (using change product key). Andy.
You should be ok. I have installed a clean copy of windows 7 (using an upgrade disc) and then entered the key afterwards on a customer's machine and it worked fine. The windows version you installed should match that of the key (premium, pro etc) - Just give it a go and see!!
I suppose if I do hit a snag I can always contact Microsoft as a last resort as the key is legit from a new unused upgade pack.