I have a laptop [Toshiba Sat Pro] and basically it needs to be re-loaded.

I have backed all contents and would like to clear and start fresh... what is the best method to go about doing this?

Will I need to obtain original OS software to reload?

Once installing the OS, will this over-write original contents?

Advise me on best method please.

Mant thanks

Most PC's and laptops ship with restore disk that will restore your HD to the way it was when you purchased it. If you have one use it. If not contact the manufacturer and they can likely provide you with one.