Red Rings of Death! or is it...?

Hey guys so this is what's up. I have 3 Xbox 360s with all the same problem it seems..1 was mine others where families that don't want any more or whatever. But all 3 Have the Rings of death. First off I opened and cleaned out all of em. Still not working.. Then I bought everything I need to repair. I removed all the x-clam replaced with screws and rubber washers scrapped off gently the old thermal paste applied new and all that. I even switched out the DVD-rom drive and still none of them will play!? Now here is a tricky part... When I turn 1 on it will start up and moments later only 2 red lights will come on. Then shortly after it will turn to just 1 red light??? What dose this mean and dose anyone know a solution? Thanks a lot!