@ Butters.
Thanks you reply, I didn't know about the Linux issue.
Now I tried PM Alexander2010 from this thread: [Only registered and activated users can see links. ]
He might be able to help unbrick Linux devices, but haven't been active on this forum since 22nd of January 2016,
so I don't have too high expectations that he will reply.
And yes, I manually enter preboot by holding the screen when powering on.

Now I also tried connect Nuvi 5000 to Linux computer, but still not possible connect as mass storage device.
Maybe there is some way I can delete map file from device via SD Card ?

@Jeanet
I tried loading full Europe NT, and Nordics (365 MB) on a 4GB SDHC Card.