It happens often that with Shift + C, since it’s center cursor and fame all, it does this two things at the same time, that you have an object very very far away and Blender trying to frame it, takes the viewport view very very far away to a point you can’t even see the grid. So in the outliner select and object and with the period key in the numpad center it to the view again and figure out which object is that you have very far away.
