Dell Latitude E 6400

​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.​