There are lots of questions about drive wiping on this website. See this search.
You can either change the password on the machine by using a tool like ntpasswd, or boot with a bootable CD like ultimate boot cd. There are other bootable CD’s like Knoppix that can give you access to the data stored on the hard drive. Another option is to remove the drive from the computer and slave it off the drive in another computer and access the data that way – or put the drive in some type of drive cage and attach to the USB port.
There’s not a simple solution here and will take a lot of time and effort to get the results you are wanting. Good luck! Hopefully you have a local IT contact that can help you along with this.