I tryed to partition Windows on my MacBook Pro to install Microsoft products and I was unaware that I needed a Windows installation disk and the screen is stuck on "No bootable device -- insert boot disk and press any key" and I had the Mac OS X installation disk in the disk drive and it wont eject. I shut it off and turn it on and its still stuck on the same screen. How can I get back to the way it was before I tryed the partition?