When I turn my iMac on, it doesn't start. The chime chimes, but nothing else. So, I start with an external drive. The internal drive shows on the desktop, but doesn't on 'Startup Disk'. I think it is dying. With 45 days of AC+ left now is the time. Should they(Apple) replaces the drive, how many chances are there that I could pay a difference and get a SSDF instead? AND are there TB3 cables? What seperates them from TB2?