Computer occasionally not turning on

First off I apologize if this is in the wrong section as i did not know where to put this.Anyway, my computer (windows 7 64 bit. x2 250, 4gb ram) occasionally when powered on the screen simply shows the screen saver. I then must manually power off the computer and turn it back on where I am greeted with a question where i select delete restoration data which it does and then starts properly. WHat is wrong with my system? THanks for any responses