IDK wtf this modwii app that you speak of is, but this thread is about ModMii, so lets keep on topic.
The issue with the game most likely was not due to the softmod, but related to the data on hdd somehow becoming corrupted, maybe from when you have plugged it into your windows pc, but you never know.
You can use ModMii. Just run the wizard and tell it that your wii is a virgin and follow all the steps in the generated guide. You do not need to, and also should not attempt, to unsoftmod or virginize your wii ever.