If not anyone else, then one thing I'd check is whether you have something (security software or other thing) that blocks youtube videos (these are all songs on youtube). A way to test that is to use a different computer or device (smartphone or tablet) and see if you can see the songs on one of those other devices (and if you could not, then what do they all share in common, like a security software? Can a friend's device or smartphone see the videos?).