For some reason, I read something that I could speed Fedora Core 3 up if I shut down some unnecessary programs with "service configuration"... well.. I did. and now I can't use any devices.. when I try opening volume control, I get: "Sorry, no mixer elements and/or devices found", when trying to open Gnome sound Recorder, I get: "The Application "gnome-sound-recorder" has quit unexpectedly."
I'm pretty sure it was caused by something I shut down using service configuration.

What might have I shutted down? what might have gone wrong?
Thanks in advance.

One possibility: udev

The udev program creates hardware device entries "on the fly". If those files don't exist, you are definitely going to run into problems in a hurry.

It's not that..
Still.. very strange.. I can still listen to sounds and all.. but I have no access whatsoever on the volume control and a few programs which use microphone and speakers.

Has anyone ever experienced this?

You might have whacked the alsa server. It is not strictly necessary for programs to use the alsa daemon. They can still send audio data directly to the audio device. Though, I must admit, I'm not sure if that's a common thing. I would hope not. Anyway, the alsa daemon does handle audio (ALSA = Advanced Linux Sound Architecture).