Minecraft Crash on launch, strange activity in task manager

When I start the launcher all is well, when you click the button to play the game the Mojang window appears as normal then crashes after a few seconds, there has been a couple of times that the game launches to the main menu then crashes. Whilst looking in task manager when loading the game I noticed that minecraft appeared in the list twice. So I clicked one and selected end task and the game started normally. However, on some occasions, it would close both instances and shut down the launcher.