Problem on Preview window, it doesnt show anything
(sorry for bad english)
So, Im a new guy on After effects and I got a little assignment from class. I wanted to do a greenscreen on a stopmotion and a video, so I import my files, create a new composition but it doesnt show anything on the preview. I goes gray, like there is nothing there, and when I move on the timeline, it goes black. I already reinstalled the program and restarted my laptop.

here are my laptop aspects if it helps:
- Procesador AMD A8-7410 APU with AMD Radeon R5 Graphics 2.20 GHz
- RAM installed 8.00 GB (6.96 GB usable)
- Operative system type 64 bits, procesador x64
Does anyone know how to fix this?
