Sound gone after updating to Mac OS 8.5.x

Kim Andersen lost all sound on her PowerBook 2400 after upgrading from Mac OS 8.1 to Mac OS 8.5.1. The startup chime is heard, so it is clear that the basic hardware is working, but no sounds occur after startup is over. Checking settings in the Monitors & Sound control panel, deleting Sound preferences file, and zapping the PRAM (all suggested solutions) did not work. Based on postings to Apple's Discussion Board, others have had this same problem with an assortment of other Mac models (see a, b, c, d and e for examples). Doing a clean reinstall of the entire Mac OS is a last resort that usually works.

[By the way, this has happened to me, but only occasionally and only after a system crash. After I restart a second time, sound returns.]