Happened several times already. Can’t say exactly what i was doing, but i assume it happened after i zoomed in. Now my screen is grey and nothing works ( i tried changing clip start and end ,pressing num 0 and all combinations with it, zooming in and out, going into wire mode, even hiding all active objects, but i am still in a big grey nothing )
Select an object in the outliner and focus on it in 3D viewport using the View -> Frame Selected (Numpad period in default keymap), then snap the 3D cursor back to scene center. This particular issue with view getting corrupted should be fixed in 2.82, though sadly not its real cause.
To that end, somehow, I see your cursor got snapped to oblivion (‘nan’ coordinates). Do you know what you did to cause that? It’s a nasty issue and it’d be good to know the cause to pass on to the devs.