Chosen Solution
I have a mid year 2010 mac book pro that I just replaced the battery on. It worked great the first day but now it won’t power on at all. What could be the problem?
You have to look at what has changed, and what has changed is that you have installed a new battery. I would remove the battery and see if it powers on via AC adapter. If it does, you know what the problem is. I wouldn’t normally expect that a battery would cause a laptop to not power on, but occasionally they can cause odd issues, especially with 3rd party batteries. If it still does not power on, we can go from there.
