pismo tolls a bell instead of starting up

All of a sudden my beloved pismo won't start up anymore; instead I hear the ominous sound of a bell that tolls 4 times. Is this the dreaded death bell of legend?

However, something is starting up: I hear a faint buzzing sound, and the green light above the keyboard is glowing (constantly, of turning on and off). I succeeded in starting up two more times, once by pushing the reset button (and making the necessary backups), and once by starting up from the install disk (I'm running OS X.3.9), which I then used for a scan of my hard drive that turned out to be in fine condition. Since, the pismo did let me down.

I suppose the tolling bell must be a giveaway for the experts; if so, please tell me what to do! I'm very fond of this stylish machine.