Since the only part of the loom that isn't protected by fuses is the starter circuit, it may be that the wiring has been mucked about with at some stage. For a cable to overheat that badly you need two faults: an excessive load and either a wrongly-rated fuse or it to be connected without a fuse at all.
As overheating may well have damaged adjacent wiring, I'd recommend getting a complete loom from a breaker.
The stuck caps-lock key is probably a separate fault.