
In my case, it was something simple. RealPlayer 11 was the cause. Presumably something to do with the "stream catching" feature. Granted, it is a cool feature that will let you rip YouTube videos, songs from Pandora, and more... but the damn thing my computer virtually unusable for 3 days. I dragged the app to my trashcan and all my issues were resolved instantly (didn't even need to reboot).
I'm not sure if there was a setting or config in RealPlayer 11 that could have been switched to remedy the problem, but if you are having similar problems you may want to see if this is the culprit.