If you are running Windows (7/8/10), there is no option to "restore to factory settings" like there is on an iPhone, for example. You will have to reinstall Windows from a disk or .iso file.
What you could try to do is download a key reader (Magic Jelly Bean KeyFinder https://www.magicaljellybean.com/keyfinder/ ) and find the product key of your installation of Windows.
After that, go to the Microsoft website and find the .iso download page. Windows 7 -> https://www.microsoft.com/en-us/software-download/windows7
Type in your product code and you can download Windows 7.
After it is downloaded, you can either make a bootable cd /dvd or USB, or just run the installer from inside of Windows. IF YOU WILL BE OVERWRITING PARTITIONS, MAKE SURE TO BACK UP ANY DATA THAT YOU MIGHT NEED IN THE FUTURE!!!!
And also, any Product keys (such as Microsoft Office) need to be written down unless you want to purchase MS Office again.
Hope this helps...