It's unprecedented, for a plane to just disappear with no distress signal or no whereabouts whatsoever. There are so many conspiracies it's incredible. Going to go through some of them.
Military shot it down:Possible cover up, however that means that there was shooting, the pilot would have enough time to communicate back, and there's no way (I think) that Malaysian ATC can cover that up. Plus, satellite images would've seen a small blip of a explosion, they found nothing.
Act of Terrorism:There's no point in doing this if the group doesn't come and admit they did it, terrorism is done to influence people or to catch the attention of the government. No one has admitted anything.
Complete disintegration:Once again, not impossible however incredibly improbably. For a whole Boeing 777 to disintegrate would surprise me, and would surprise most people, which is why most people have ruled this out.
Tried to turn back to land and got lost: Very probable in my opinion. They could've lost all their communication systems and nav systems. You have to remember this was at night and at night, you lose all sense of direction, they could've got lost very easily and just flew on for hours not knowing which way they where going.
My idea: Cabin de-pressurization: Improbable but then again, possible. The cabin de-pressurised very quickly making everyone pass out therefore stopping all communication. Problem with this is, that the plane even if everyone died, it would still broadcast it's position through it's squawk and other things. Rolls Royce and Boeing have yet to confirm or deny whether the engines stopped sending signals so we don't know about the engines yet.
Truth is absolutely no body knows, it's incredible how this plane just disappeared off the face of the earth, and, the way this investigation is going, I doubt we'll ever know.