Freezing, Power Management, And Funny Beeps



I have a Powerbook G4, and I took the following from the System Profiler:

Machine Model: PowerBook G4 15"
CPU Type: PowerPC G4 (3.3)
Number Of CPUs: 1
CPU Speed: 1 GHz
L2 Cache (per CPU): 256 KB
L3 Cache (per CPU): 1 MB
Memory: 512 MB
Bus Speed: 133 MHz
Boot ROM Version: 4.5.3f2

A couple of times now, today and yesterday, the computer has frozen, and even when I would hold down the power button for a few seconds to try to restart, it wouldn't restart like it normally would (and I hardly ever, if EVER, had an unexplained freeze on this computer - I could usually track it down to an unruly application, but not this time). These past couple of times when it has frozen, holding down the power button shuts it down, but I would have to hold down the power button several times at least, maybe five times, before anything would happen to indicate that it's not dead. After the fourth or fifth time in a row I would hold down the button, I would see the indicator light flash (it's right on the hinge underneath the words "PowerBook G4,") and I would hear a tone that sounds a lot like when you update the firmware on an old-school iMac, if you know what I mean. Then, I'll hold down the power button again, and then it will finally start. But it takes a while to get from seeing the grey apple to the login screen.

Maybe this is related: My battery has a short life, and the computer unexpectedly goes to sleep without warning to conserve itself when the battery percentage would say something like "85%" charged. When I would plug it back in and wake it from sleep, it would say "0%." I tried following some steps I found on several help sites including resetting the PRAM by restarting the computer and holding down opt+apple+P+R. I also took out the battery with the adapter plugged in while holding down the power button a few times (but I don't remember exactly everything I did or in what order - this was a couple of months ago). Oh, and none of this helped - same short battery life, and it still "thinks" it has 80% charge before unexpectedly going to sleep.

Do I have a PMU issue? Is so, what can I do to fix this? Is my 'puter screwed? Should I back everything up and reformat? Or is it totally irreparable?

I would appreciate any help! Thank you so much!