Check link below and also links within that link:

http://www.ehow.com/how_5022486_reset-ad...

more info needed. do you mean for the first time? or are you trying to use a second hand computer?

what are the circumstances etc

you need an informative question to get an informative answer..

You need to ask an daministrator to make your account an admin one.

I am using a Mac NOT a pc.

I guess you would ask the owner.

no