Chosen Solution
I have just replaced the battery using a kit from iFixit, because it had been routinely powering down with more than 50% battery. I have just tried to start it for the first time since the replacement, and it makes the startup chime but the screen stays black and it does not turn on. The fans seem to come on very briefly when it chimes. The light on my MagSafe was initially amber but turned green after only a few minutes, as though the battery was fully charged. I have tried resetting the SMC by holding cmd+option+shift+power for ten seconds, and resetting the the PRAM by holding cmd+option+P+R for ten seconds. The latter makes a second Chime or even a third but then nothing happens. Please tell me I haven’t killed it!
Did you check the battery and charger before you swapped out the battery? I recommend CoconutBattery and getting a snapshot so we can check if the battery, charger or charging logic needs service. Without that it makes it tough to know which way to go.
