objects in scene view are flashing (appearing and disappearing suddenly),my game objects in scene view are flashing (appearing then disappearing)

i am using 2D mode with orthographic camera.. my problem is that when i add an object to scene view, it disappears (except its handles).. and suddenly it reappear for a second then disappear... although in camera preview it appears perfectly.. same is in game view.. also when i hit play, objects appear for second then disappear forever!!! note; i tried to build and run the project.. everything was okay and appearing well.... note; i tried restarting unity several times but no result!! this problem is facing me for several months ago..

,when i add a game object to the scene view, it doesn't appear (except its handles), then after some seconds it flashes (appears for a second then disappear)!!! on camera preview, every thing is okay.. my objects appear perfectly.. In game view also i have same problem.. when i hit play, objects appear for a second then disappears!!! note: if i build and run the project.. all objects are appearing very well.. note: i am using 2d mode with orthographic camera