I ran into the same problem. One issue might be OpenCV is created for Python 2.7, not 3 (not all python 2.7 libraries will work in python 3 or greater). I also don't believe you can download OpenCV directly through PyCharm's package installer. I have found luck following the instructions: OpenCV Python. Specifically:
import cv2
, and assuming no errors print cv2.__version__
Alternatively, I have had luck using this package opencv-python, which you can straightforwardly install using pip with pip install opencv-python
Good luck!