This is a problem I've been having for a couple weeks now. My fix has been to restart my computer entirely but it shouldn't be that way. Nothing will play in Premiere. I press the space bar in the timeline and in the source window, I get nothing. I'm running premiere pro CS6 in OSX 10.6.8. I have no clue how to fix this issue. It's killing my productivity. Like I said, I restart my computer and that's a temporary fix. Any help on a permanent fix would greatly appreciated. Thanks.
Have you tried a different keyboard?
Do Macs use drivers for KBD devices?
Maybe a conflict with another device or app ( eg Wacom Tablet...)
Can you playback using the mouse controls in the Monitors?