I can't sign into iMessages on my Mac. I just bought it off of Craigslist so I might just do a factory reset (is that a good idea?) on it. The message reads: iMessage Password Please enter your password for firstname.lastname@example.org I try to log in and it continues on a never ending cycle. Someone @ Apple support communities mentioned to change something in Keychain but I didn't see anything that would help there. Suggestions?