I have a strange problem with youtube. Videos that I could see before now I can hear only the sound. And this is happening since last week end. The funny thing is that videos with advertisements works good. I tried to run again the computer or also to restart my computer from a certain point in the past losing the latest updates and I thought I could work. It worked but only for one day.
As a temporary workaround, you can try one, or both, of the following:
1) Right click on the player > click Settings > Disable Hardware Acceleration > Refresh your Internet Browser
2) Try closing your browser and re-load the video.