A few things come to mind:
The three beeps indicate bad RAM or, possibly, a bad logic board. See
Intel-based Mac Power On Self Test RAM error codes and
Power Mac G4: Computer Beeps Three Times. Even though the second article refers to a G4, the error code is the same.
You are evidently having occasional
kernel panics, which is consistent with RAM or logic board issues. See also
Resolving Kernel Panics.
Assuming that the computer is running long enough to do this, go to the Apple menu and click About This Mac. That will tell you the specific OS that you are running. If you then click More Info in the About This Mac window, you'll launch System Profiler and will be able to see everything that you would ever need to know about your Mac.
