Complicated Problem

I am selling my Macbook Air.

One year ago, I this Air was briefly submerged in water.

A few weeks ago, the screen went nuts and I was told my AppleCare was voided due to water damage.

It worked fine in clamshell mode with a displayport adapter.

In preparation for selling it, I tried to format the drive. I did this (wrong) by starting the computer while holding option or option+r, don't remember which, and going to Disk Utility. From there, I selected the drive and clicked "erase".

When I start the computer now, it cannot find the hard drive. I get the folder with the question mark (it's the only thing I can make out on the bloody battlefield of flickering lines that constitutes my internal display).

This sounds like an easy fix, but there is a problem: clamshell mode doesn't work anymore. I have checked all the obvious things: power supply is connected, usb mouse is connected, used two different displayport adapters. Unplugged and re-plugged everything. Attempted to restart holding option+r, just option, or nothing. No clamshell.

Displayport connection isn't even recognized in that "second display" way that it's supposed to when it's not in clamshell mode.

Also, my computer won't go to sleep. Related? I don't know.

 

I already found a buyer, and anyway I'm not going to sell a computer with an incorrectly formatted hard drive. It's too easy for the buyer to recover my files.