You can try to repair your navi by yourself:
1. Download the navi soft, for example from HERE
2. Burn it to the CD on the lowest speed (before burning check if it is in Mode2)
3. Swith the ignotion of your car off, close all doors, open trunk
4. Wait till your navi device goes to sleep (led on the navi swithed off)
5. Disconnect two cables from the back side of the navi
6. Wait for 15-20 minutes
7. Connect again two cables
8. Swith the ignition on (Pos.1)
9. Put the CD (step 1-2) into your navi
10. wait till navi update starts (it could take for a certain time)

If this will not help then really would be better not to repair but to change to the MK4, it's very simple, just plug&play.