root password confusion - new user

Hi,

Quick rundown for you:
I have just purchased a netbook with ubuntu 12.04 installed, the previous owner said he had not set up any passwords on the user account.
I have myself set up a password but am unable to use some of the functions as it keeps telling me 'authentication is required' and to input my 'password for root' It will not accept the password that I have set up for my user account.
I have twice gone through the 'shift@ bootup/recovery/reset' procedure and put in different passwords but It wont accept any of them.
The user account doesnt seem to have administrive rights so I cant break out of the cycle.
I have done some quick research but it looks like I may do more harm than good as there are warnings against doing certain things and conflicting information. I have tried following a guide to use sudo but upon entering the password that I had set up on the user account it either says 'sorry, try again' or 'john is not in the sudoers file. This incident will be reported!? I cant add john to the sudo users as I have no administrive rights?!
I have always been a windows user and this is my first ubuntu experience so any help offered will need to be in a simple form please!
Thanks in advance