Solved!! I found the solution on the BO2 FAQs. It is not that i had to reinstall the program, i already had all files. For both problems, they proposed this solution:

Fix: You are missing redists the game needs to run. To fix this download and run the following redist installer then restart your pc and it will be fixed: https://github.com/ChxseH/Redist-Installer/releases/download/latest/Redist-Installer.bat

I did it, and everything woked perfectly.

I have downloaded the indicated bo1 file, i have installed plutonium, and i have linked plutonium to the folder of the game. Whenever i try to open bo1 zombies or mutiplayer, i get this messages (2 photos attached + a photo of how my game folder looks). Please help!