Please make sure you have the latest version of the Unity Webplayer if you are experiencing crashes or black/white screen. The latest update utilizes the latest version of Unity and cannot run on any previous iterations of the webplayer.
To succesfully start the away timer, click out the game window (ie. the chatbox) then move on to which ever tab or application you'd like. When you come back it should calculate what you would've had if you were still on the tab. Please vote up so people can see!