I power on the Performa and the cat steps
on the apple key. The cat stays there and I
press the power button again because
the computer wasn't responding.
Afterwards, it responds, but not what I
was hoping for. It gives me a Sad Mac
with an error code of:

0000000F
0000000D

What the Babylon does that mean?

Naughty but Nice

Probably, it means that you have an Operating System installed on this Mac, but for any reason the OS has become corrupted.

I'm afraid you only have one possibility: reboot the Mac from a CD or from a floppy, and install the Operating System again to make it properly work.

OK. I shooed the cat and restarted. It started normally with NO sad mac. Then I shut down, powered on and immediately pressed the Apple key and the Power Key. It gave me the exact same Sad Mac. I restarted it without pressing the key combination and it restarted just fine. It ahs something to do with the key combination which is the Interrupt Key combination... the same thing would have happened had I pressed the Interrupt button.

Naughty but Nice

A sad Mac occuring not long after the power button being pressed usually indicates hardware failure; or imminent failure. A sad Mac later on after pressing the power button (i.e., during booting or in a session) indicates, usually, software error.

Probably a bad RAM stick, or you can at least hope that, as a bad mobo/HD will cause a bigger headache.