Thank you both for your suggestions..
Accidentally I ran this command :
dd if=/dev/zero of=/dev/hda bs=521 count=1
to delete the boot loader but found that it had deleted all my partitions
So, I had to reformat the hard drive and install windows into it.
After that, I also installed fedora core 6, but it installed with some problems. I will post my enquiry in a new thread.