Can't see tiles...

I was following the 'crash course' and it said to run game so I did and then all the tiles had disappeared as well as Mambo! Only the goombas were there...

So I went back to the scene editor and when I went to the tiles tab the tiles were gone and Mambo was gone from the actors tab and only goomba was there!

I have saved the game and am trying to open it again but it is taking f o r e v e r ! ! !

Has your problem been fixed?