If there is no sound in QuickTime 6 for Windows and other programs are working properly, you may need to change the "Sound Out" setting for QuickTime (from the file bar in QuickTime --> Edit --> Preferences --> QuickTime Settings --> Sound Out). Try switching from "DirectSound" (default option) to one of the "waveOut" settings (specifically, the waveOut setting that references your installed audio driver (I.E. "waveOut: Yamaha SXG Driver"). Restart any active QuickTime windows for this change to take effect
There was also mention of changing your audio sampling rate and re-installing Quicktime. You can get it
here
Good Luck !