I have been trying to turn on my MacBook Pro but it won't fully turn on. It probably happened because I hadn't turned it on in months, but when I turn it on, it just goes to the loading screen which is all white and has the loading icon under it...

I have tried to plug it in the charger over night and leave it on the loading screen to see if it would turn on, but it didn't turn on at all and was still on the loading screen. I looked up to possibly take out the battery and put it back in, but when i got my Mac book open, there was a warning on it which said not to take out the battery.. So not really sure what else to do. I didn't do anything to mess it up, it just hadn't been turned on in awhile. Not really sure how that affected it.