Are you finding the "ATmega328 on a breadboard (8 MHz internal clock)" under >Tools>Board>?
If not, here is the path that it should be: C:\Users[youruserprofilehere](My) Documents\Arduino\hardware\breadboard\boards.txt
Are you finding the "ATmega328 on a breadboard (8 MHz internal clock)" under >Tools>Board>?
If not, here is the path that it should be: C:\Users[youruserprofilehere](My) Documents\Arduino\hardware\breadboard\boards.txt