1st you will need a service manual, you'll never get it apart without one.
HP doesn't have manuals "on-line". Another reason to buy a Dell.
The power plug is not the pin, it's the entire receptacle. You need the right size and there are hundreds of different sizes. It looks like this:
If it's attached to motherboard, new mobo is either $400 or $700. If the computer will be trash, anyway, start taking it apart. Take photos so you'll remember how to put it back together. This will be a big project and will take many hours of work. It's not impossible, if you have the patience of a watchmaker and the precision of a diamond cutter. Everything is really small. If you can unsolder the connector, you can find one somewhere.