Rang Rover L322 Infotainment system dead.

Hi guy's looking for a person/company that knows their way around one of these factory systems. Have checked the usual suspects for corrosion and water ingress bot no problems that I can see. All fuses are good, relay in boot is good and power at all the units. However, don't get any hint of a red light down the MOST connections in the boot. Head unit screen is blank and no orange light. Can get head unit to power up by removing the fuse waiting a while then replacing. This action brings up the screen with the logo press top of screen the top right button then get key pad showing. Entering maintenance code 753 get me to test screen press self test and it switches off back to blank screen. Based in Hertfordshire but willing to travel reasonable distance for help.