Try it in a working Gameboy (or decent emulator like BGB) and press left or B, if you want to know what it should look like. When you press B or left it makes the screen dark, and that's absolutely everything it does. Of course it wouldn't work if the B and left inputs are broken. The point of the test is to read the buttons in a way that gives the button more time to settle in case maybe, maybe that would help. And not surprisingly, it didn't. But it had to be tried, right?
The damage that I think you've gotten, from your description, comes from you inserting or removing the ribbon cable. This shorts two of the pins, where one is the LCD supply voltage and the other is the combined B and left input. (Yes, that's how it works.) This fries this input INSIDE THE CPU. Replacing the connector won't do any difference. Get used to it and see this as an opportunity to explore mGB or whatever else doesn't require B and left. Or alternatively, piece this display board together with a fully working CPU board. (And make sure the power is off this time.)
This MAY still actually be physical damage, but then you should likely be able see the damage. Example:
http://chipmusic.org/forums/post/96847/#p96847
You should see damage on the 4th connection from the left. However, again, I don't think this is your problem based on your description.
