Firsoffall you can undo the view change... yuo find it in the menus of the panel (previous view). Or you can reset the perpective view. you can always select using outiner and hit a.
Or you can remedy the cause. it can be one orf two things. but as im not in connection with my database of tips/tricks i can only remeber the most trvial case (ayway i have only encountered the second thing once in my entire life so id imagine its not that common altough some people do say it can be):
Your scene is too big... This causes the view to align correctly but nothing shows up because the near faar clipping planbe is too small increase the lot of them. (open atribute editor for your camera)
Or then theres one renegede object that has either it bounding box wrong or is located very faar away. Either move it closer or fix the bounding box.