Macbook Facetime HD camera (not working)

Dear mac users,

I have a macbook pro 15" Mid 2015 Retina with a facetime hd camera that doesnt work. Every time i launch facetime or photo booth the camera screen is pitch black and the indicator green dot is just flashing the whole time. I suppose it might be a GPU issue since i opened the macbook a couple of times through the years to upgrade the ssd, change cpu thermal paste and clean up the fans. It could be something else but based on the description hopefully you can give me an insight if i can do something by myself to fix this issue at some point.

Regards.