(T) Next project on my pile of junk stilo - Fix dead connect nav+

Has anyone any experience of these failing. Mine used to work fine, but now I just get the Fiat logo at startup, then the screen breaks up into blue squares. Does not turn off with the power button.
CD player will not spin or eject disk.
I have removed it from the car and am powering it through the ISO connector only.
I assume these should start up in that state, and it does not need the Can bus before it will initilaise and at least show me an error message.
I have unpluged CD player, GPS etc to see if it makes a difference, but it is still the same.
Does anyone know what the initialisation procedure/ tests for these is. Also is it possible to recover it if the firmware is corrupted.
Any help apreciated.

just a software update/re-install me thinks.

the CN and CN+ do have their paddys every now and then

How do I do that then?
CD drive does not spin, so putting a CD in with new software will not help.