Restoring Studio 1735 to factory settings

Hi, I have a Dell Studio Laptop 1735 and would like to restore it to factory settings. I read that this can be done by pressing F8 when starting up the laptop and clicking "Repair your computer" from the Advanced Boot Options menu. However, I don't have the option "Repair your computer" in this menu so I guess I need a recovery disk or something.  Where can I buy one of these from? Can I get a link to buy the disk online? EDIT: I am from the UK and I am using Vista.

Then you will have to ring dell support from the link below,

http://support.euro.dell.com/support/topics/topic.aspx/emea/shared/support/dellcare/en/byphone_prod?c=uk&cs=ukdhs1&l=en&s=dhs

other methods of contacting them below,

http://support.euro.dell.com/support/topics/topic.aspx/emea/shared/support/dellcare/en/contact_technical_support?c=uk&cs=ukdhs1&l=en&s=dhs&~ck=anavml