Did you hard-reset it? If not, do that now: [Only registered and activated users can see links. ]. Better still, clear nonvolatile memory: [Only registered and activated users can see links. ]. Back up your favourites first if you wish to restore them later because either will clear all user data.
If that doesn't help, post with more detail such as whether your map is showing in .System folder as gmapprom.img when connected to PC in Mass Storage Mode, and also if it's showing and is checked enabled in Tools>Settings>MyMaps. Usually you can at least see the basic basemap info on the map screen even if there are no detail maps on the unit. Look for the Basemap info in Tools>Settings>System>About too, or in .System folder in MSM for gmapbmap.img.