Are yaar, there are three possibilities:
1. if you deleted linux files or partition accidentally and want to keep linux then you can reinstall it again and it will restore the boot loader.
2. If you haven't deleted linux yet and the grub installation itself is corrupt then boot your computer from your linux cd/dvd into rescue mode. There do a chroot to your installation and then run grub-install to reinstall grub.
3. If you have deleted linux and just want to have only windows on your computer then boot from the Windows CD and enter into Recovery Console. From there run the commands FixBoot and FixMBR. This will reinstall the Windows bootloader.
For all of these methods you need to boot from your cd. If you have selected Harddisk as the first boot device then you'll have to change it from BIOS. At the time of booting, press f2, f8 or whatever is the key combionatio for entering your bios (it generally shows in the last line on screen while booting ) and from there set the First Boot Device to CDROM. Save and exit setup and insert your cd to boot from it.