Great news for you [so far, but not 'out of the woods' yet by any means]. Next is to make a backup of the unit's internal files and then we'll delete them to see if the unit will work. As this unit cannot process 'if error' command, we need to go step at a time.

First make a backup of the current SD card contents to your PC. Then remove update.log and Last_ID.bin. Make an additional empty root folder named 'Backup' [no quotes]. Change the update.txt content to:

copydir,0:/GPX/,1:/Backup/
reboot

It will take a while so be patient, use at least a 2GB card, preferably 4GB or more. You should have a full copy of the internal files in the Backup folder of the SD card after the reboot.

If that works, backup the card again to your PC and again remove update.log and Last_ID.bin. Now do this:

ergn,48
reboot

Hopefully afterwards the unit will now be visible in Mass Storage Mode. If so create a Garmin folder and after another reboot connect it to WebUpdater & MapUpdater to replace missing files [or use GarminExpress if you wish instead] add a basemap and you should be good to go.
If not, post again and i guess we'll have to erase 41 [or whatever kunix suggests]. Late here, so logging out now.