What make of PC is it? Usually you can find the manual on line on how to re-set to factory settings. Most well known makes also have a hidden recovery partition you should be able to access on boot-up.
Usually, with the recovery disks, you need to boot the PC so you can insert the first disc in the DVD drive (bios is usually set to boot from CDs now) then restart the PC and it will boot to the disc. You then follow the prompts. Before you attempt anything let us know the make and model of the PC.