Did anything happen or just one day it worked the next it didn't? Looks like the controller's gone a bit crazy which doesn't usually happen on it's own, but when it does that's the end of it. If you're an expert solderer you could replace the controller chip but firmware would be an issue...
The easy option would be to desolder the switches and use them in the case and plate and add some wire, some diodes (cheap) and a Teensy or similar microcontroller ($20 or less) and learn how a keyboard works - they're quite simple really. Then you'd have a working fully programmable keyboard, just without the flashy LEDs.
If you want the backlighting to work you'll need to find/make a PCB that matches the layout of the plate - I can't work it out from the back but it looks like a 75%? Not sure what options there are for that but surely some.
Edit: Keycool 84... Looks like
this PCB is the right layout?
