can't log in

My interns use my laptop at work. I noticed it was still running today when one of them left today, so I decided to restrict internet permissions for their user. When I logged out of the admin to log into the intern user, it went to black screen, Darwin. It prompted me to login, which I did and it said "welcome to Darwin". I didn't know what to do from there, so I typed "reboot". It went to the blue screen and then back to the black screen prompting me to login to Darwin. I couldn't get any further, so I decided to start up from the disc. My only option was to "archive and install" or "erase? and install". I didn't see any other options - they may have been there, but I didn't see anything. Installation was successful.

It starts up, goes to the log in screen, and I can't log in to either user. It won't accept either password. How do I get into my computer? What happened to my passwords?

I'm weeks behind and need to get this thing working asap!

I just scratch the surface on OS knowledge, so you might need to "speak slowly" in order for me to understand.

I appreciate any help. Thanks.

Boot up from your OSX disc. (hold down the C key with the disc inserted and power it up or restart) Set a new Admin password from there.