Welcome to the Dell Community [NAME]  What valid key??? Was it the one on the laptop??? Was it one that came with the W10 DVD??? Does the key match the version of W10 you installed??? W7 Pro will only activate W10 Pro etc. Best regards, U2
I am a retired Fed Govt retired computer guy. I picked up a Dell latitude e 6440 at a yard sale. I cleaned it up and it ran great. I tried to install windows 10 DVD. It loaded fine. I tried to activate on the 6440  using a valid key. I was rejected saying I needed to use my companies activation server. This latitude is about 10 years old and it has no corporate Identification on it. I searched and failed to to find a work around. Any advice would be greatly appreciated.
Dell Latitude E 6400