Sat Nav Problems MK3 to MK4

Hi i have a 03 Vogue which suffered from the leak in the rear of the car killing almost everything in the boot satnav drive include. I have replaced almost everyhing but when it came to installing the new upgraded MK4 Satnav all i got was a black screen on the monitor. The screen was still backlight but nothing came up. I have been running for about 3 months without any sat nav drive installed and have had the basic low res screen. But when i installed the satnav all i get is a plain black screen. i dont even get the update screen when trying to install the latest software. I have sent the unit i had back and im waiting for a replacement so if anyone has any ideas to what it could be id be extremly grateful especially if it was my fault and have damaged the unit as i dont want to make the same mistake twice.

Kind Regards

Johnny