If you want to delete GRUB and a linux distro you may have in a partition and bring backWindows bootloader
boot to windows and delete the partition you have linux and GRUB installed, if you restart the windows will fail to boot because GRUB, poof! gone!
After doing that you can do 2 things to get Windows boot successfully:
1. place the Windows7 CD, select your language and click on repair, then click onCommand prompt and type: bootsect /nt60 C: (or whatever drive letter use your system) - this will bring back Windows bootloader and system will boot successfully, done.
2. Download EasyBCD from here... and then execute it. Once you open the program go to: BCD BackUp/Repair tab select "Recreate/Repair boot files" (in case that your boot files are ruined somehow (this step can be skipped)), then select BCD Deployment tab and under "MBR configuration" click "Write Windows7/Vista bootloader to MBR" or "WindowsXP bootloader to MBR" according to what you have. Then you can restart your computer, Windows should be boot without any problem.