gameobjects do not appear in the build game

i am new to unity. i build the first project which was roll a ball and i complete it without problems. but after i build and run it all my object do not appear i see the text i made and as i try move the player without seeing it the count counter increase which mean the player is there and the pick ups and the back ground are there too. i tried change the main camera position but still it is grey. i tried making a new project which i only contain object with no scripts and focus the camera on the objects to see if the problem was from roll a ball project only but also the new project show nothing. please help.