XP's starting problem after removing Vista from a dual boot

The Problem:-

This is a scenario where Windows Vista in the active partition and it's a dual boot between Windows Vista and Windows XP.Now if you have removed Vista either by deleting the partition or formatting you will find that XP is not starting.

Resolution:-

Just perform a repair installation of Windows XP to restore the booting problem.

Reference:-

How to perform an in-place upgrade (reinstallation) of Windows XP
http://support.microsoft.com/kb/315341