how can i restrict only single user to a particualr windows exe.
You don't really give enough info for a specific answer, but there are a number of options, depending on whether it's your own code, or an existing .exe:
For any .exe, you can use file permissions to deny "Execute" permission for all users except the specific one - in an administrator account, get properties on the .exe file and go to the Permissions tab to set this.
If it's a commercial application, you could install the application only on that user's account (Most installers offer a "for all users or only yourself" install option)
If it's your own applicaqtion, you could write code into your application to read the current user and refuse to run for other users.
You could write a "launcher" application that will check the user and then run the actual program only if the user has permission.