Only two things happened between the time FLV last worked and when I first discovered that the sound was gone on FLV player.
1. I installed Microsoft updates KB961371, KB973346, KB971633
2. I installed magic Jack on my Desktop computer
When I discovered the no sound condition on my desktop I checked my laptop - FLV player worked there.
I already have magic jack on it. But just to be sure I uninstalled Magic jack on the desktop anyway.
I also uninstalled the 3 Critical Updates listed above.
Then I noticed that emptying the recycle bin did not produce a noise either.
What fix it (for me - you may need a different solution):
Go into control panel, sounds..., Audio (Tab): Look for something like modem #0 line playback
set this back to Windows default audio or what ever used to be there.
After that, my FLV player sound and Windows sounds can back to life.
I hope this is your solution as well. Good luck.