sorry is this has already been posted, i did search but couldnt find anything.
mine happened today. i was making a new partition, as i am considering doing a linux from scratch project, and i requires a ext2/3 partition. i made it, then tried to boot ubuntu. didnt work, so i booted windows, and deleted the partition. rebooted. GRUB error. could not boot ANYTHING. i was like: "OH NO!!! what on earth have i done??!!
then i remebered fixmbr, and booted back into windows.
scary stuff.