Hi, I am running 64-bit too, and with exactly the same cards, Asus ATI hd4870! I reinstalled the drivers
now, and disconnected the second screen. Haven't tried listening to music yet, but I will do it now and you will hear from me in about 5-10 minutes I guess. Haven't tried the media player no, but if that works and the others don't then I don't know whats wrong. I should also mention that when I for instance try to watch the IGN videos from E3 (haven't tried any other movies yet) the computer also crashes.. But I will try now.
Another problem, my counter-strike:source will not update.. It downloaded, but now it says "download starting..." and it never starts, I've tried everyting; given steam admin rights, rebooted steam, and paused the download. Still nothing happens..
Thanks for a quick answer!