bought a computer from a manufacturer but it had a dell windows license sticker and the computer is not a dell

The maker of your machine may have bought a bulk batch of Licence keys with CoAs from Dell. So long as it is activated and passes Windows Genuine Advantage, you won't have a problem.

Google for and download a utility named MagicalJellyBean Finder and use it to extract and decrypt the actual Product Key then check to make sure it matches the one on the CoA on your case.