If you formatted your drive on accident, there is still a chance. Get another computer, and mount your old hard drive on it. Then, use this software to try and recover your list data: https://www.powerdatarecovery.com/lost-partition-recovery.html
It may or may not be successful at recovering your neccacery but it should be enough to at least get some of your data.
If it can't recover the OS, use a bootable USB stick to re-install Windows. I can provide a guide when you tell me your version of Windows.