Can somone install a computer game that has already been installed on another computer?

I gave a computer game to my friend, he installed it and played it, but didn't like it. I was going to sell it, but can the costumer also install it even though it has been installed previously. Is this possible?Can somone install a computer game that has already been installed on another computer?
yes, but you can't reregister itCan somone install a computer game that has already been installed on another computer?
It really depends on the game. For example, I have three copies of Call of Duty 4 installed at home, all registered from the same CD. The code is unique to each CD, all it does is just prove to the installer program that you have a valid CD, and that you didn't pirate the game from a website. The code shouldn't have any limiting factors on what computers it'll run on. Still, games vary, and not all games use this technology. My guess is if you were able to install and run it on your computer and your friend's, it'll work for the customer. Have the customer contact you if any issues arrive that prevents installation of the game on their computer or inhibits full use of the game, as the game you're selling may be one of those rare, stubborn ones.