Unusual issues with both wordpress and my theme (wp-admin related)

I am getting some weird issues with wordpress for no apparant reason. Some of them I know are related to the theme I made, but one other thing seems to come out of nowhere.

First the theme related issues: When I try to save a page/post, log in or out, or make any decision whatsoever that requires the page to save something, I end up going to a white page whenever I save. I also get a fullscreen page whenever I try to upload media when setting featured images. The blank-page thing goes away when I switch themes, but the fullscreen upload keeps happening.

Then there’s the really weird thing: The visual tab of the editor is unclickable. I checked everything but can’t come up with any solutions. Only reason I can come up with is because I tried to manually put tinymce up, but I don’t overwrite anything at all.

I tried to fix this by replacing my wp-admin and wp-content with the original folders as they come in the wordpress download, but no help.

Any idea on why these issues are occuring? I already know this doesn’t have to do with my plug-ins.