I had a dual-booting laptop with Linux Mint and Windows XP on it. After deleting the Linux Mint partitions, it failed to boot into XP because grub can no longer find the MBR. This was the error message:
error: no such partition grub rescue>
Solution:
Boot into SystemRescueCD and run this command to create a new MBR:
lilo -M /dev/sda mbr
Note: My XP resides in /dev/sda.