|Have you the most up to date versions of Adobe Flash and Shockwave players?|
If not, I suggest you uninstall the old one(s) and install the newest. Also, Flash uses an inordinate amount of cpu cycles on some systems, so I suggest that you have as little running in the background as possible while attempting to play.
Internet Explorer and Firefox use different Flash players, IE's depends upon activeX and Firefox's does not.
"Doin' right ain't got no end." Cap'n Red Legs