I would second that comment about power supplies. Nearly every problem (rare) I've ever had with my many Pi computers can be boiled down to weak power supply or the USB cable that feeds power... Keep cables in mind. All my problems in the past 24 months have been cable related. Even 12" long cables I have used in the past have become the 'power limiting' defect. These same cables still test and work for many things, just not power. New trusted, well made, large gauge cables have fixed my issues.