google for "{your model# here} disc image" or 'recovery disks'; that you could download but triple check it for viruses & the like. HP charges $10 for theirs.
You were supposed to make yours when you setup the laptop, are you sure that you don't have the disks somewhere?
I always do this for my customers and include them in the box, so if someone set this up for you and gave it to you as gift, check the box it came in. You might get lucky.