the screen is displaying a jumped mess after power-up (though certain screens such as the boot screen are entirely normal). IMAGES: https://imgur.com/a/jx7PUMv
The power supply is only 2 years old. Fan is upgraded and mechanical HD removed for SCSI2SD. I've reseated all connections and given everything a look over, no obvious signs of wear inside (e.g. bulging, leaking, smoking...)
I am willing to pay for repair if anyone is able to point me to a technician who may be able to help. Based in London.

Better living everyone.