I'll hijack this thread, then.

My PowerBook 100 also has problems.

It used to boot up to a ? Disk, but now, instead…



After some diagnostic tests, it appears it has to do with the Capacitors.

Ah, yes. If they don't chime, try plugging in a pair of headphones, the speaker shares an internal connector with the display.

Edit:

Forgot this link: http://www.vintage-computer.com/vcforum/showthread.php?37083-Powerbook-100-Restoration/page3