When starting a new project in AE, all of the sudden jpg's aren't recognised and exports are black.

Hello, whenever I start a new project with AE something weird happens. I am no longer able to import jpg's normally (there will just be a black pictogram) which I can bypass by selecting ALL files and then just JPEG. But the weirdest thing is that I cannot export anything anylonger. It's simply black or black interwoven with some minor glitches of color (also the size of the file does not match up to the length and codec). However, when I go back to an older project the problem dissapears; I can import everything normally and exporting works fine as well. I have tried rebooting, reinstalling, unplugging external drives etcetera. I have no idea what I can do about it. I have a mid 2014 mac with 16gb ram and everything is fully updated. Hope someone can help!