Hmmm, curious.
Check your terrain folder, only the terrain folder. Do you see a temp.map file? If not, search your files for it. The temp.map is the temporary terrain that appears in the Map Maker when you load it. If it's not in the terrain directory, it doesn't load the default terrain. Also check that you have the temp folder in the terrain folder, it will contain tempGates.cfg, tempMaterial.cfg, tempObjects.cfg, etc. Again, it is the flat terrain that appears with the Map Maker initially.
If that isn't the case, then look for the default folder. Make sure that all the corresponding files are there as well, they appear to be regular map files (terrain and heightmap images).
The only other solution I can think of is looking in the resources.cfg that is located in the main FeralHeart directory. Open that up and check to see if there are "breadcrumb trails" that lead to the terrain folders and back. (They look like: FileSystem=media/terrains underneath a [Terrains] )
Do you have any mods that could have altered your maps? Objects, particles, ENB or graphical mods? If so, manually delete them.
If all else fails, manually delete FeralHeart (press delete or drap and drop into the recycling bin) and all the files related to it (keep a backup of the group map, unless you have the download link itself). Sometimes the uninstall leaves files behind and when you reinstall it, they stick around and mess with everything.
