freeze and then three beeps

[Eric]

hi: this morning my powerbook froze up.  i shut it down by holding down 
the power button.   when i restarted, i heard it start up but then i 
heard three beeps (or tones) and the  light that pulses when asleep was 
blinking.  the screen did not light up.

i shut it down again and zapped the pram which seemed to do the trick 
the second time (after taking out the battery and unplugging).   i ran 
fsck and it fixed a lot of stuff.

my question is what do the three tones (not sure how else to describe 
the sound) mean.  i've never heard that before.

this is a 667 dvi.   thanks.   eric