Here is what I see in your file that is strange (as said above, it may be due to some imported file and/or some later transform by you or others), and I'm quite sure it's causing all kind of weirdnesses you experience in your file:
the camera is gigantic, both in scale and size, and its location seems strange, values are too high for typical blender files.
Also you see the camera clip values are ok (default values), but the interactive view has way too big values: 1.5 and 10015 !
the grid, too is gigantic: 300 while the standard is 1 ?
and also the wheelchair (eg: the selected wheel) seems gigantic, although the scale is 1...
As you see, there is something wrong: I could correct your scene, like this: first of all, I reset "wrong" values of your grid, view, wheelchar, camera, lamp guessing they could be some hundred times higher than "normal". Where "normal" is a coherent range scale of all scene elements that makes the blender files view and manipulation (including camera view) beheve predictably, and "well".
- the wheelchair: I selected the controlling empty of all the chair elements, then I changed its location to 0,0,4 (almost grid center) and scaled it down all by 0.01 (that means 100x smaller): this makes also all the parented wheelchair elements to be transformed as the emtpy.
- the camera: I changed its location to +30,-8,+45 and set its size back to 1, and scale to 1,1,1.
- the lamp: I changed its location to -5,+12,+45
- the grid: I set its size back from 300 to 1
- the view: I set view clip to the standard 0.1 - 1000.0 range
Now, everything seems to have disappeared! It's not, of course, its just that everything is reset to "standard" dimensions, and your view is still as previously: pressing the keyboard's "home" button (ie: "show all") should make your scene be visible again, well in the center and with proper view, grid and camera settings. And now I have this:
Let me know if you need to download your file corrected, but it would better that you try to repeat my steps above, so you can practice for similar situations in future.
Please don't forget to add details about how you got that file (import, transforms), if possible, because it will let a trace for other users in similar situations...
Here is the corrected file (now with a single 3d view area):