I applied the 2.0.1 jailbreak recently.

After resetting all my data on my iphone, it doens't boot anymore because it gets stuck in an endless loading screen.

Is there a way to turn off the iphone so I can do a recovery in the DFU mode?
Resetting it with the Sleep+Home Button doesn't work because then it just restarts automatically.

As soon as the screen goes black, let go of the Sleep+Home buttons...

It should stay off. Good luck