If it's for Windows 10, the option can be found in the StartUp repair lists that show up if you power off by switching the machine off without shutting Windows down first. Turn it back on and do the same again and those options will show up. Click on Advanced and you'll see Refresh and Reset.
Refresh sometimes behaves like Reset and all you files are removed so back up even if it means taking the hard disk out and slaving it to another machine.
For earlier versions of Windows, it's getting harder to find ISOs at Microsoft's website so you have to buy a new Product Key and install Windows 10
For a Toshiba c55 laptop and it has been a real joke trying to find or figure out. My WiFi my HDMI doesn't work plus a few other things. I tried to put this on here yesterday but it keeps taking me to all kinds of places.
Some has the recovery discs on the OS You have to make copies from laptop if You can still get on Your Laptop go to search and type in recovery cds! see what you get! if You do have it is a lot easier to copy them to DVDs then cds because it takes a lot of cds! If You don't have a recovery, then You will have to purchase recovery cds from Toshiba! Or if You are familiar with Linux, that is Your best route, because You can get a free Linux Mint OS from the Linux Mint website! Linux has come a long way! Regards!