After doing some searches, I find that:
From the PS3 main menu:
1. Settings->Sound Settings->Audio Output Settings
2. Change it from HDMI to Digital Out (Optical). I do NOT have optical hooked up on my PS3, so if you have it hooked up, you may want to unhook it.. probably shouldn't matter.
3. I left what was defaulted: "Linear PCM 2 Ch. 44.1 kHz" and 48kHz
4. Right on the D pad (X selects/unselects options) to move to the next screen.
5. A confirmation page, hit X to Enter, saving the changes.
6. Start up a game, you shouldn't hear any sound (as expected)
7. Exit the game, then go back to Audio Output Settings and switch back to HDMI. I selected "Automatic" for "method for setting the output format."
8. A confirmation page, hit X to Enter, saving the changes.
9. Start up a game, you should now hear audio with your game (once again). The problem is most likely caused from having switched your PS3 to a different TV for a period of time.
Hope that I will work for you