Keyboard not working, mouspad working sort of, computer turns on

I have a 2010 MacBook Pro I bought off eBay for parts and repair - the listing showed the flashing disk icon, so I thought it would be a simple repair.

It came without a disk, but I was easily able to install Mac OS X on a disk.

During the installation process - I notice the trackpad tracks okay, but clicks on the trackpad do not work well. And, once I get to a screen that requires text input nothing works on the keyboard. Also at boot-up, pressing the OPTION key to cause a selection of the disk does not cause that selector to appear, instead it simply boots off the disk.

UPDATE: After plugging in an external USB keyboard I was able to finish the installation. And holding down the ALT key on this keyboard did cause the drive selector to come up after powering on the computer.

UPDATE: With the computer booted the keyboard backlight is working.

UPDATE: As noted below the keyboard ribbon cable is fully inserted, as evidenced by the power button working to turn on the computer and the backlight working.

UPDATE: Using the Notes app, I can verify that NO keys on the keyboard work, and the CAPS LOCK key does not light up.

/UPDATE

For the trackpad I am pretty sure of what to do. The trackpad holders are bent in a way implying the battery pack had swollen very badly. The seller confirms the battery had swollen. I’m sure it’s a matter of adjusting the screw and other stuff related to the trackpad and it might work well.

The keyboard…?

The ribbon cable for the keyboard seems fully inserted.

Currently am stumped over what to do next.

The seller claimed there was no liquid spill.