Cannot access Open Firmware

Hello,

I've been having a recurring problem with not being able to wake my system from sleep. From the research that I've done on the forums, there are a number of potential solutions, such as resetting my PRAM and SMC, which haven't solved the problem.

Another solution (found in a response to http://discussions.info.apple.com/thread.jspa?messageID=10652526), is to reset the Open Firmware settings (using the commands: reset-nvram; set-defaults; reset-all). The problem that I'm having now is that holding down Cmd-Opt-O-F while starting the system won't bring me to the Open Firmware command line, despite repeated attempts.

Is there something else that I need to do to access the Open Firmware command line? After resetting the PRAM, I also re-selected the Startup Disk (I read somewhere that this may be required to access Open Firmware after the PRAM reset). I've also read that Intel-based Macs use EFI Firmware rather than Open Firmware. Does this mean that I need to do something different on my Intel Mac to get the same effect?

Thanks!