PRAM replacement - or other issue?

More likely your battery is shot! This series needs power to hold its settings, here a dead battery won’t help as it’s acts as a drain messing up the boot process even though you have it plugged in.

Give this a try to get you hobbling! Follow this guide through Step 3 disconnecting the battery Remplacement de la batterie du MacBook Air 13" début 2015 with nothing plugged in press and hold the power button for a good 15secs to fully discharge the logic board. Now plug in the MagSafe charger. Your system should spontaneously startup! Let it fully boot and do a clean shutdown. But before you do that! Once the system is running download this app CoconutBattery it will allow you to see much more on what’s going on with your battery and charging. Now after shutting the system down plug your battery in and with the MagSafe plugged in you should be able to boot one more time. Now launch CoconutBattery take a snapshot of the apps main window with the battery info tab open and post it here for us to see.