Then open the Media Player Classic (shortcut MPC) and press "O". You will get into the options. Go the to "External Filters" Menu and then press "add" on the left. Add the AC3 Filter as well as the CoreAVC Video Decoder (by klicking "add filter..." and then point the program to the .ax files which were installed in the beginning [CoreAVCDecoder.ax] & [ac3filter.ax])
Now you just press "OK" and restart your MPC. Now your ready to watch 720p movies even on a weak machine (like mine )!