How can I fix this booting up problem with my old Macbook?

Hello,
I bought my first Macbook in 2007. I haven’t touched it since 2014 when I replaced it. Now, I want to try to sell it (or donate it) but want to see what’s on it first/transfer files.

When I hit the power button, it gurgled for a bit and then made powering up sounds. However, nothing happened on the screen. I clicked and held the power button again and it made the “powering down” sound.

I don’t know any of those tricks of what buttons to hold while booting up, in case it’s a simple fix like that! Any ideas? It is plugged into the wall and the charger light is on. And yes, I tried the screen brightness key, smarty pants. :)

Thanks in advance!