How do you reboot your laptop to its original factory settings without a back up disc?

There's usually a disk that comes with the computer that restores to factory settings - not a backup disk but a stand disk similar to the drivers disk

Otherwise check the make of the computer - some of the newer ones come with an onboard factory restore (click a few buttons when its starting and it restores)

Most modern notebook models have a partitioned hard drive (2 virtual hard drives from 1 physical hard drive. The restore disc saved on the machine. Please F11 or F12 when booting up to find it.. If not found you will need to find a Windows OEM CD for manufacturer machines..

What brand laptop is it? Hp, Dell, Acer, Toshiba? How old is it?

First if you plan on restoring to factory you might want to download Paragon Boot manager...

Once that is done reboot, then when boot manager comes up select factory image...

Then just follow onscreen instructions.