I'll bet you recently upgraded your OS. Bad News -- CS 5.5 isn't recommended for El Capitan. You found out why.
This has been happening to me as well with CC 2015. I think it's a graphics issue. If you are like me you are you running two monitors with your layers in your secondary monitor. If that's the case, the fix I found is to drag your layer stack to your primary monitor, click the playhead, then move back. Seems to work fine after that.