Can't boot from 10.5.6 install disk

[bad2pay]

First timer here. I bought a used G4 MDD 1.25 dual FW800 recently. Was pre-loaded with 10.5.6. I thought that I would add a hard drive. After attempting to format, it rebooted to a gray screen with a MacMonitor icon. If I hit "option", I can get it to progress to a blue screen w/ padlock asking for a password. I only remember setting a user password. I believe this is asking for an admin password.
So, I thought that I'd get the 10.5.6 Install disk to reset the password. I can't seem to boot from the Install disk! I've tried holding down the "c" key at startup, (also the "option" key). No avail. Completely frustrated!!!

 

[grue]

Open Firmware password. Pull one of the RAM chips and zap the PRAM

 

[bad2pay]

thanks for the reply.

I am at Open Firmware. I typed "reset-nvram", then it asks for a password, which I don't have. What now?

 

[NoNameBrand]

http://support.apple.com/kb/HT1352

Grue almost had it - you need to zap the PRAM three times, apparently:

1) Add or remove DIMMs to change the total amount of RAM in the computer.

2) Then, the PRAM must be reset 3 times. (Command + Option + P + R).

 

[bad2pay]

Fanfriggintastic. Back in business.

First rate, thanks guys.