Appreciate all the effort and help guys. We've sorted it! With the mention to basicly duplicate the Nuvi by copying the GarminDevice.xml etc. I basicly just re-did the entire cure/format/original firmware again. Installed the voice files etc. Copied all those files to a USB stick and let MapUpdater run it's course using the USB Stick. Installed the map fine.
Now I had to copy/paste the files back over to the Garmin. THIS IS WHERE WE HIT THE PROBLEM. All files moved over except the reasonably large gmapprom.img (even only UK/Ireland 366mb map) if ever attempting to copy this over directly to the .system folder results in power down. I then simply pasted it to the root of the Garmin and re cut-pasted it back to .system where it needs to be. Now my Garmin finally works again. I must tell you im surprised since i smashed it to the floor a long time ago in anger of this problem.
But still what's the problem? some sort of bad storage on the Garmin in a certain area? bad sectors for example.