[Brad Bullock]

I had the same problem. I have CS3 and a dedicated machine so I know it was internal. I had added a firewire connection (PCI) to use a new compatible capture device.

I found it had to do with the device control. As of late I do not use machine control. If machine control is “on” the timeline will not play (other than audio as someone stated). I have to either unplug the firewire RCA capture device input or turn off machine control.

Hope this helps.