I have a Imac running 10.5.8. I have forgotten the admin password which won't let me log in as admin or install or download any software. Do I have to reset it using the "Imac OX X Install" disk? I tried that, but when I insert the disc, restart the Imac, and press C at the reboot I get a "?" mark. Also I have like 10 other accounts on here also. Does it matter what account I use when I do this? Thanks!