If your computer freezes or has problems starting up, sometimes it offers the option to reset to factory conditions, or it will ask you to choose a restore date, and then resets everything to that date (unless it picks a date for you, usually a few days previous to the current date). That would work to fix any damage done by a virus if you had gotten one somehow. If you are running Windows 10, you do not have to worry about backing up all your personal files, because you can do a factory reset without losing any of your files such as images, videos, or documents. You might lose all your bookmarks, though.