CPC 464 Keyboard and joystick fault

[Plutesio]

I purchased an Amstrad CPC464 which seems to have immediately developed a critical fault.

I initially set it up to briefly test and everything was working fine. Today I decided try out the joystick that was included (Cheetah125+) in the sale. 

I ran "oh mummy" to test it. The first input (pulling down on the stick) worked fine until the character hit the bottom wall, and then no other inputs registered. I the tried the keyboard and no inputs registered. The game continued to run, the computer didn't crash, but no inputs from the keyboard or joystick would register. 

After powering off and on the Amstrad boots into BASIC as normal, however no keyboard or joystick inputs register. I have tried both with the joystick connected and with it disconnected.

I'm guessing the joystick has somehow damaged something.

Is anyone able to guide me through some checks with a multimeter to identify what has been damaged? Or is it a case of figuring out which components relate to the joystick port and replacing them one by one?

Any help appreciated. I'm absolutely gutted!

[Plutesio]

TL;DR

After attempting to use joystick my Amstrad no longer detects any keyboard or joystick inputs. Which components might be involved?