bheemamahesh ..i do want to ask u one thing..have u ever made an image of your XP system?? I m asking this becoz "if u want to keep fedora and XP both in working condition then u can copy the system image to C:\(or root directory) mounted folder so that windows may come back again in working condition...
IF you had not made any image then dnt worry..try finding out "rescue disk" for Kaspersky or Bid defender. Rescue disks are live disks. It will surely bypass the GRUB. Once bypassed, scan your windows partition in search for viruses and after the process ends try booting up ur XP.
You are asking about GRUB? It is difficult to explain you in simple language. But i m giving u a link which is very useful:-
http://www.dedoimedo.com/computers/grub.html
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