Q: boot errors?

Boot up while holding the Option key down until you see the boot manager, do you see this...

<img src="http://km.support.apple.com/library/APPLE/APPLECARE_ALLGEOS/HT1352/106482_2.jpg">

Firmware password protection in Mac OS X ...

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

It would block usage of all the startup keys, like C, N, T, D, CMD+s, CMD+Option+p+r, CMD +v, Option boot will show a lock, and Shift, as well as booting from anything but the Hard Drive.

Force Removing Password Protection

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).

http://www.securemac.com/openfirmwarepasswordprotection.php