Can\'t start playback

I've been having a problem where ProTools LE randomly will stop letting me play back a session. The start and stop buttons on the Transport bar light up like normal, but all tickers stay at zero and no audio is played. Once this happens, the problem persists until I reboot my iBook. I have no idea what could be causing this. Any input would be appreciated.

what is the mach,cpu ,ram, ect. and was it working before. And did you add anything new

I'm running an iBook with a 700 MHz G3, 384 MB RAM, and an Mbox. I've had the problem pretty much as long as I've been using ProTools.

This behavior could be due to an extension conflict. Create a Mac OS Base Extension set, enable the following extensions and restart the computer: -Digidesign Control Panel -DigiSystem INIT -Digidesign Direct I/O -Digidesign DSP Manager -Digidesign Stream Manager -Digidesign USB Driver -Open Music System -USB Floppy Enabler Brent