sound issues

Sounds like when we move the volume slider in taskbar tray, toggle keys etc cannot be heard through headphones/external speakers connected to headphone jack, but media playback sound is fine, but no such problem in built in speakers, bluetooth headsets/speakers. Also this problem seem to be only...

suddenly refuses to play any sound (numlock, capslock etc / music / ). strangely, when i open any video player, the seek bar doesnt move too. itunes says audio/video configuration error. opening playback devices in sound and configuring/ testing sound shows that another application is using...