I followed Apple's instruction to reset PRAM ("Press and hold the Command-Option-P-R keys before the gray screen appears.") and the only thing that happened was that my Mac rebooted repeatedly until I stopped holding the short-cut. After releasing the keyboard OS was loaded but without any startup sound and my original problem remained (see Original problem)
I found out that not being able to reset PRAM may be caused by the user password, so I tried to disable the password request but this did not work either. This seems to be because of FireVault which I deactivated a couple of hours ago. My system is still encoding so it might take another couple of hours until I can see whether this approach was useful.
Does anyone have another advice?
Original problem: No sound, no micro
My MacBook Pro (2.4 GHz Intel Core 2 Duo, Mac OS X Lion 10.7.5 (11G56)) was on stand-by all the night. When I opened my Mac this morning I had no sound and my micro did not work either (A call via skype failed (I could not hear anybody and they did not hear me) but the camera worked. I cannot hear music via iTunes nor any other application. Also I cannot hear the click sound when one tries to turn up volume.). Therefore I thought resetting PRAM would be the solution but I failed in doing so as described.