I'm running on a Dell Studio XPS 1640 and this problem has been around as long as I can remember, I just haven't been able to pin it down until now. Whenever an application (e.g. a media player, Youtube in my browser, etc.) tries to play an mp4 file or stream using the default Windows decoder for it, my system freezes up completely (no response to anything other than holding down the power button). This sounds a lot like this other post, but my system isn't nice enough to wake up after some number of seconds, even after I tried manually adding the registry key (TdrDelay) mentioned in one of the links.
I've tried both the latest drivers listed on the Dell website for my system and the ones here on the AMD website, but both suffer from this problem, and I don't know of any others. I do know that this has to be the drivers somehow, because by uninstalling all of them I can prevent these freezes from occurring (though video just refuses to play as a result).
My media player of choice (Zoom Player) is nice enough to display a filter graph for what it's hooked up to, but unfortunately I can't use it to figure out the specific decoder that's causing the problem because of the symptom.
For the time being I have redirected all of my current software away from the default Windows decoders, but I would really like to know how to either disable said decoder on a system level, so it can't be accessed at all, or, even better, get the damned thing to work properly.