Black Screen When Using the Brush Tool

Hello everyone!

I just downloaded the Adobe After Effects few hours ago, I'm still learning how to use it, I did a couple of things but I got a problem and can't keep going with it, as I said, I'm new with this app, so I'm gonna try to be the most precise I can be to describe my problem.

I may did modifies something in the toolbars or something and now when I try to draw with the brush tool, the screen gets dark and I can't see my original video.

Before, when I used to draw with the brush tool, I could see my original video, go frame by frame and draw on it, but now for an unknown reason I can't.

Also in the Project window (top left) there's nothing there, and before I used to see something like (Project = ''File Name'').

So when I'm on Composition I can see everything but when I go to Layer and start drawing I lose the image and get a black image to draw on it.

I really want to use this software, please I need your help.

I can provide screenshots or a video in need, thank you so much.

Have a great day.