Resetting the NVRAM
From Mac Guides
You actually shouldn't ever need to do this. But sometimes, hacks that you install (such as the iBook screen spanning hack) or system instability prompts you to desperately turn to resetting your NVRAM to the defaults. Perhaps you may even be selling your Mac and want to leave a completely clean slate behind you. The possibilities are endless, the reasons are few. However, it has been accepted in the Macintosh community that errors with OS X can be fixed on occasion by resetting your NVRAM. Preferably, you should repair your permissions first as well as perform other troubleshooting steps.
While booting your Mac, hold down the keys Command + Option + O + F. This will boot the computer into Open Firmware.
At the Open Firmware 0 > prompt, type each of these lines followed by the return key:
Your computer will restart with NVRAM reset.
NVRAM can also be reset by resetting the PRAM.