Yes, you will have to reinstall the OS.
For your games, if they are Steam or Origin, you can probably move those elsewhere, and after the reinstall (incl the Steam client), move them back.
The steamapps folder is what you're looking for.
"Browse to the Steam installation folder for the Steam installation you would like to move (C:\Program Files\Steam by default). Delete all of the files and folders except the SteamApps folder and Steam.exe. Cut and paste the whole Steam folder to the new location, for example: D:\Games\Steam\"
https://support.steampowered.com/kb_article.php?ref=7418-YUBN-8129