Uploaded Images Not Showing

Hello. So, I installed a new theme in my website, but I don’t know what happened that now everytime I upload an image from my computer to the media library it won’t appear, not there and not in the website. If I go to the link of the image, I get an internal server error.

But the strange thing is that the other administrator of the website is uploading images just fine. I’m admin too. Any hints on what may be causing this? thanks