Why does this laptop turns on briefly, and then shut off?

My best friend has an HP Pavilion. It was her fathers, who passed away about three months after he purchased it.
It’s been sitting in a bag for about a year and a half now. It wasn’t turning on at all because it needed a power cord. We bought a universal one tonight at Best Buy, and the laptop will very briefly turn on and then turn back off. We know the cord is getting power to it, and the fans are starting, but we can’t figure out why the laptop won’t stay on.
She said that it was never turned off properly. So maybe someone just put it in hibernate.

What could be the cause of this and how do we fix it?

Thanks!