Youtube page loads, but videos won't play

OS X 9.10.5... Chrome, Firefox, Safari... I've updated Flash Player to the latest version, cleared history and cache, restarted 3 times, and still, the videos on Youtube will NOT play! The page loads completely, I click on a video, a black screen appears with an 8-dot circle that goes round and round, but the videos never load! I even tried logging in to Youtube. NO GO.

Anyone have any idea how to fix this??