Well my best guess at this point is reinstall mirc and check options sounds and rerun those codes I posted before.. I didn't mention it before but the main volume/mute control and mirc volume/mute must BOTH be set to on (they have separate settings in windows volume control) ...if none of that works.. pardon the pun but sounds like a hardware issue.. I can't believe the little speaker died but that would be the only component you could fix reasonably.. I would find it hard to believe the beep circuit went bad and nothing else on the motherboard..
