Seems I got the same problem, only with Mavericks. I have a gray progress bar on launch, and at 10% or so my computer shuts down. I can't boot with the 'c' or Shift key pressed - well, I can, but it doesn't do anything.
So I'd love to get rid of rEFIt that's in the way ! And go back to using the 'Press alt on boot' to change partition (I have Windows 7 installed as well as Mavericks).
Thanks in advance for your help !