If sugestion from Caty don't work try this:

Windows XP

Click Start
Click Run
Type regedit in box
Click the + next to HKEY_CURRENT_USER
Click the + next to Software
Click the + next to Garmin
right-click on the folder Mapsource
Click Delete
Close the Registry Editor
Restart the computer
run MapSource.exe and you will see map

Windows Vista / Windows 7

Click Start
Type regedit in the search box
Click the arrow next to HKEY_CURRENT_USER
Click the arrow next to Software
Click the arrow next to Garmin
right-click on the folder Mapsource
Click Delete
Close the Registry Editor
Restart the computer
run MapSource.exe and you will se map