I know it's not mpc.. but atleast you can watch videos in peace now <3
If you really want to get mpc working: I think you need to reinstall all the stuffs that mpc came with.. think I saw the video acceleration in the install options...
For games... directx 10/11 might lock your comp, directx 9 works fine. Also if you pop directx 9 on instead of 10/11, your mining speed increases.
Disable hardware acceleration from firefox advanced settings too.