After Effects composition turned black

• I've got the same problem, it's like if I have to many layers with a few effects the whole screen just goes black

This happened to me too a few times..Very annoying. Nothing works. I have to start over.

I changed some AI files and they automatically reloaded into AE, like they do.

I hid all the layers(with the eye icon) and then turned them on 1 by 1. Some layers were visual, but some(AI) layers weren't. So I think maybe it's because I changed the AI file some things got messed up.

I've also restarted twice, moved my clips to a new composition and started a new project but this still happens.

I'm not clear what you are saying. all i say is an MP4 file at the top of your stack, which is of course an opaque layer with not Alpha channel. if it is supposed to serve any function beyond just sitting there, you have to set the relevant options or apply effects. It seems you are not understanding something very basic here, It's just not clear what you actualyl mean based on yopur lack of info and awkward description.

Mylenium