This has been put down to a sound problem (i.e. having DivX sound drivers installed) but i'm not so sure. When i first started playing i had the no sound problem, uninstalled divX and reinstalled the windows sound pack which cleared up the sound problem straight away. But i got totally stuck at this bit 2, eventually i reinstalled windows 'cause i was so desperate to play more.
I was using XP pro, and even following some of the very detailed posts about removing all traces of divX from my HD and registry seemed to make no difference. To be honest at that point i would probably hav bought a whole new PC if i though it would let me play on
Good luck fixing it, and if you do hav to reinstall windows dont make the mistake i did of not backing up my saves, assuming they were wiped and then realising that the fresh install had left my old 'Documents + Settings' folders alone and given then new ones different names...