No charge, even after AC jack replacement

I recently purchased this device off eBay knowing that it was unable to receive a charge. In the seller's pictures the device was shown to be able to turn on, but by the time the device arrived to me it had used up what little battery it had left and is now dead.

When I plug the magsafe charger in, there is no indicator light (I have tested the magsafe on other laptops and it is working).

I have tried unplugging the battery and holding the power button for 5 seconds, and I also replaced the AC jack.

I am still unable to get any indicator light/charge at all. Any advice would be helpful!

Update: I have found corrosion on the motherboard (see pictures below). I am currently cleaning with 70% rubbing alcohol (will run to store later to try and get higher). Any advice on cleaning this further?