Premier Pro playback suddenly not working

I was just editing a video when suddenly the playback stopped working and all videos are black when I move over them with the curser. In the media libray I can still see the thumbnails but I can't click on the videos. The program itself is not frozen but I can't do anything. I'm not really sure how else to describe it. I tried all the tips I could find about playback issues but so far nothing has worked. I hope maybe someone has another idea for me to try? Thank you!