Problem:
No sounds were heard in PD11 from any project.
However (1) System sounds could be heard in headphones. (2) WaveEditor played sounds. (3) .MPG and .WAV files created previously by PowerDirector played sound in Windows Media Player.
For Information: PowerDirector v11.0.0.3625 was installed on 26/1/2014

Fix:
Select [Playback] menu option
Select {Adjust System Volume} - Slider display showed sound on lowest level
Slid slider up

Result:
Sounds heard! HP p6315uk, AMD Athlon(tm) II X4 630 Processor, 2.81 GHz, Windows 7, 4Gb DDR3-SDRAM (1333 MHz), NVidia GeForce GT610