first of all: Personally, I don't play the windows version of SWC. I sometimes play SWC on windows but only the android version in an emulator (i.e. NOX). So I have no personal experience with windows account recovery.
These guys here wrote some IMHO very useful info about the playerprefs-file on windows computers:https://sites.google.com/site/swcommand ... /resources
Obviously your playerprefs-file has been overwritten/deleted. This tiny file contains the login-data to your SWC account. The most important data in it is your player-id (visible in-game) and a player-secret (just in this file). When it gets lost, the game can't login to your existing account anymore and will begin a new account with new player-id and therefore start from scratch.
This is no problem if you actually do BACKUPs on your PC. This is what everyone recommeands IMHO and on a PC you don't have the restrictions of mobile devices which often make it unnecessary difficult to create "real" backups. You only need one file from the backup and that is the playerprefs.dat file described in the link above. As the playerpres.dat only contains the login data, the backup can be of any time in the last months where you played the game. After restore of that file you game will be up to date.
As a home user, you usually make backups on external USB drives, a NAS or even in a cloud (online backups in clouds are often limited and incomplete). They either create file archives or complete images of your disk. An old backup/copy of all files in your user folder to another disk/folder naturally also would help in this case.
A "Windows System Restore Point" (If we're speaking of the same function) is not a general file backup. It is a method to restore your windows settings (driver/registry) in case the system gets unstable/unbootable. To my knowledge, it doesn't save the data of any additional apps/programs.
But Windows offers a "File History" function. (Which has to be enabled)http://www.pcworld.com/article/2974385/ ... ature.html
If this was already enabled at the time of your problem then you might be safe because it backups all files in the Users folder where also the playerprefs.dat file is situated.
If you have no backups of your computer anywhere then it will be near impossible to restore your game. Some person with computer knowledge might try and scan the sectors of your hard disk for old deleted copies of the playerprefs file. (You can take the search strings from your current playerprefs.dat) Most certainly the data is overwritten, but you never know, the file is not big so there's a remote chance.