I've had bad topcases that caused irregular behavior related to sleep mode and rebooting. If you have another topcase available to test it might be worthwhile. Also, Apple laptops go into sleep mode due to various magnets throughout making a connection with each other, and if those magnets in the screen and body of the computer are in the wrong place or are not present, this can also cause bizarre behavior (computer continually going into sleep mode and then waking up, etc.) Particularly there are two magnets in the screen frame I know of related to this, so if by chance your screen has been swapped out, it's possible a magnet is missing.