That does sound like corrupt PRAM, if you wound up in Open Firmware (the mac-boot prompt). Check your battery voltage - should be 3.6V minimum. If the battery is OK, then press the Cuda reset button once, wait 15 seconds and try a reboot.
If the HD has been replaced sometime in the machine's history, there is an excellent chance it is incompatible with a flaky IDE controller chip. Rev 1 motherboards don't support slave drives or UDMA-capable hard drives. You need an old 2GB or smaller drive like the Mac shipped with, or you need a PCI drive controller card. The rev 2 MB is usable with newer drives up to 128GB.
If the HD has been replaced sometime in the machine's history, there is an excellent chance it is incompatible with a flaky IDE controller chip. Rev 1 motherboards don't support slave drives or UDMA-capable hard drives. You need an old 2GB or smaller drive like the Mac shipped with, or you need a PCI drive controller card. The rev 2 MB is usable with newer drives up to 128GB.