Black playback and unable to change renderer under file>project settings>renderer

Hi,
On one of my edits, I have been unable to view the playback of my video... The playback is just black. I've watched a few videos on how to fix this, and they reccomend changing the renderer under file>project settings>renderer, but the button to change the renderer is not available either. The playback quality is set to 1/2 resolution. The playback on my other edits are fine, just not this one. I've also cleared the cache. What are my next steps? Thanks!

