MacBook Pro :: Can Only Hear Sounds From Messages

I hear the various sounds involved with Messages in Lion 10.7.3, when sending a msg, receiving, contacts becoming available etc.  I am not hearing *any* other audio at all: No sound from Chrome with: Facebook videos, Youtube, Soundcloud or Vimeo.  No sound from any media in Safari.  No sound from any media in iTunes.  No sound when playing files with Quicktime. No sound when increasing/decreasing system volume.I can only hear Messages sounds! Everything was working fine last night, the last thing I was able to hear was an .m4a file that I played through Quicktime.  This morning - nothing.  Where should I start troubleshooting?  I've already restarted a couple of times, will do a full shutdown and restart again.