If you did reset your computer and you had to reinstall the game, your maps will probably be gone.
I recommend you to get a external drive (Big USB Stick or external harddrive) to put the Osu folder on. The game can run on its own in its own folder, so you might just want to do that, so you can reset your PC as often as you want without losing your Osu data. This is especially important, because your replays of every achieved score are saved in the Osu folder, so you might not want to lose the future ones.