Please elaborate...
If it does not open for you:
This is not how you are supposed to use kartmaker. The correct way is by dragging the folder of where you have your sprites template edited and your character sounds loader and have the properties.ytxt in it adjusted. It will export the character as a wad or pk3 as the name of the folder.
If you are using it correctly:
Check your same location of where kartmaker located to see your wad. If it did not make a wad file, try again. You may have a typo or a syntax error in the settings file of your properties.txt file in your sprite folder. Try checking that closely. To get more debugging information, open a command prompt and locate your kartmaker folder. Then type:
kartmaker.exe (name of folder)
where (name of folder) is your sprite folder name.