Helo Pinky
You can reset (blank) the Administrator password and then start
a session as administrator.
To blank the Administrator password you have to use any third party
available tool. I recommend a Linux minidistro called Austrumi cause
it's really usable. For more info read:
http://www.petri.co.il/forgot_administrator_password.htm
PLEASE, NOTE THAT IF THE ADMINISTRATOR USED THE EFS (Encrypting
File System) ANY FILE SO ENCRYPTED WILL GET UNRECOVERABLE. SO ONLY
USE THIS SOLUTION IN CASE NO IMPORTANT FILE WAS ENCRYPTED USING
THE EFS (OR UNLESS YOU HAVE A RECOVERY AGENT CERTIFICATE AND SO ON).