I recently purchased my first macbook off of a third-party site and everything was working fine. Until, one day I notice on the imessages screen it not longer had my information but someone else's and it was locked. Whoever hacked into my netflix and/or macbook ruined everything. So I decided to do a factory reset on my macbook thinking it would help get rid of whatever it was. But it just kept going to that operation screen menu. So I took it to my best friend's brother that works at best buy and they verified that I deleted the whole system but couldn't do anything for me because they were closing. I am not sure what I should do, I need my macbook for school. Does anyone know how to fix it and get the operations system back?