I stumbled upon this post today and chose to sign up as I am having the same issue as the OP however it has nothing to do with the youtube app. I have triple checked every possible setting for auto lock (screen saver, power settings, ect), all are properly set however windows 8 still insists on locking after a certain amount of time. Oddly, the only time it will not auto lock is when I have Plex media center open and set as the active window...it will stay unlocked for days on end as long as i keep Plex open (which is a total pain). However, as soon as i close plex and give it a few minutes I am presented with the login screen where i have to supply my password. I have no screen saver enabled, the display is set to never turn off and the computer is set to never sleep or hibernate (which works fine). The only issue is this auto lock that i cant seem to get to the bottom of. I am a network admin by trade so stupid issues like this drive me nuts, hoping with a few more heads I can get to the bottom of it. Thanks in advance.