Accidentally started to delete main Europe map, stopped it, but then found device was apparently corrupted and had lost 0.5GB of memory

Ran CHKDSK to fix that and re-installed main Europe map NT v9 gmapprom.img from backup on computer. Seems to navigate OK BUT does not display street names unless I touch the street on the screen. Other maps on SD also fail to display street names, so it seems to be the nuvi rather than the map that's at fault. Tried re-installing software 5.00 via WebUpdate but no improvement. Also tried CHDSK again, but it found nothing wrong

Any help would be greatly appreciated!