Hi Lupe,
Can you confirm if the button is there? Or if when you click it, it just doesn’t do anything?
It sounds like there may be a conflict with either you theme or maybe with another plugin. It would be really great to see if switching the theme back to a default theme for a few minutes gives us back the function of adding media. I haven’t heard of this issue yet with any other users so isolating the issue is really the best way to get you the help you need. You should be able to switch between themes without any loss of data, but if you are worried I’d first confirm with your themes support team just to be sure.