Boot. Hold Command-Option-O-F.
Type reset-nvram at the promtp.
Hit enter.
Type reset-all.
Hit enter.
Reboot. Put CD in. Hold CD. Work?
If not open system, take out battery, disconnect power. Leave for 15 mins. Replace power and battery. Now try.
No good?
Turn off, take all DIMMs out. Replace DIMMs. Now try.
No?