Love my new iMac just one big issue

[njfirefighter]

Hi everyone I looked around the forum and online alot and I could not find this answer so I am sorry if this has been asked before. About a year ago my girlfriend convinced me to switch to a mac when the time came for a new computer and I grew to love it little problem when she set it up she made the account pw (yes its the admin account and yes its the only account) so now I do not know the pw. I have the mac osx snowleopard 1.6.3 disc and could not reset the pw w/ that. When I restart the computer through the option to on the disc or through the normal way and then hold down C like I instructed to do in many right ups the computer screen remains blank white w/ the the apple logo continously beeping any help on how I can reset the pw this way or any other way ty in advance!