Video hardware acceleration is not working!

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I have been playing more and more 720P+ videos recently and have been puzzled why I sometimes get stuttering as I assumed the hardware acceleration options would have sorted that for me. So I went and ran GPU-Z while playing some videos, there is never any load at all on the graphics card when playing any videos, in Flash or in my media players (KMPlayer, MPC-HC with haali splitter, VLC and WMP), does anyone know what is wrong, or how I can solve this? I did some googling but I can't seem to find anyone with the exact same problem :/

Attaching an image below, and here are my relevant specs:

Windows 7 64bit
Flash 10.1
E6600 @ 3.6GHZ
4GB RAM
8800GT 512MB (G92 version) - Tried newest beta drivers and even very old ones.

Cheers