Tangier- My first thought would be that some of the media was inadverntantly digitized to the Macintosh HD (system drive) and FCP is struggling to play the footage. Try Get Info on the MacHD. With all my software I still have 120 gb available on my system drive. If your system drive is loaded you have something on it that shouldn’t be there. The other issue might be too many applications open but I see you have 4gb of RAM so that shouldn’t be the problem. Hope this helps. Jerry