These symptoms are very similar to those that occur when the personality card is poorly seated or malfunctioning. It may, however, be caused by the wrong CD being used to install Mac OS onto the computer. The following CDs will cause this behavior:
691-1924-A
691-1969-A
691-2042-A
The way to resolve this situation is to reinstall Mac OS from the CD that came with the computer.
For more information on this topic, please see article 24503: "
Power Macintosh G3: Loose I/O Card Affects Monitors & Sound Control Panel"