Chosen Solution
So my 2014 15in MacBook Pro will hold charge, but when try to power on, it goes into boot chime loop with black screen. Backlight and keyboard lights are off. Anyone know solution? Update: installed new battery, still doesn’t work. Also, when I disconnect battery and just plug in charger, it also goes into same loop.
Unlike latest iPhones, that bootloop for whatever small reason, Macs usually do not bootloop. I’d try reinstalling the OS through a Usb pendrive or through the recovery: https://support.apple.com/en-us/HT204904 If a reinstall fails too, there’s probably a hardware issue, either RAM or processor related; either or, a logic board failure that would need a logic board repair or replacement.
