To do a repair install you boot from the XP CD. From there it will load the setup. After the setup it will give you a few options. Install, Recovery Console or something else. Choose to install XP.
I know this sounds odd but it is okay. It will show the EULA. Hit F8 to accept. There is will search for Windows installations. It should find you current install. Then it will give you more options.
You can choose to install XP again, Repair or exit. This is where you choose the repair. From there it will delete the XP files and then go thru the process of installing them again.
I do not accept support questions via EMail, PM, IM or my G+ page!
Phone: LG Optimus G Pro
Running: Stock JB from LG with Nova Launcher