Each brand has it's own method for reloading the Operating System. Most give you 2 options to reformat the hard drive, quick & long. Use the long. Post the brand and the model number off the UPC label on the back if you want the F key process for reloading the O/S.
there are also several programs out there that will over write the entire hard drive as well prior to reformatting that prevent all but the most advanced hackers from "accidentally" recovering any of your data from the HD.
When I sanitized hard drives in towers and laptops that were destined for gov't surplus, I used DBAN (Darik's Boot and Nuke) and the 'DoD 5220.22-M' method (alternating zero-fill and one-fill and a final verification pass). DBAN is free to download and use. Now I use UBC (Ultimate Boot CD), which has DBAN and bunch of other great utilities, and is also free to download and use.
