Mac PowerPC Performa 5260.
I found my alert sounds to be annoying so I turned them off using an extension called systemsquelch(?). I am unable to use real audio due to an error 50. I've gone back to my original system 7.5.5 and double checked my sound control panel following the suggestions in the appleguide. Still no sounds. when I try to adjust the volume button the menu bar flashes. My audio cd plays. Please advise.