How to Replace Missing Registry Boot Files

Windows Vista and 7
1. Open the CD tray and insert the Windows system disc. Wait for the operating system Advanced Boot menu to load.
2. Click Next and choose "Repair Your Computer" after you choose your language settings. Click the "Next" button.
3. Click "Startup Repair" in the following menu. Startup Repair runs a diagnostic check of your registry and operating system to determine what system files or registry keys are malfunctioning; then it fixes them. When the Startup Repair utility finishes, restart your computer.
Windows XP
4. Insert the Windows XP install disc into your computer and restart.
5. According to Microsoft, you should press "Enter" at the Setup screen--do not access the Recovery Console at this point, because the Recovery Console attempts to install a fresh copy of Windows XP and thereby deletes all your data.
6. Accept the license agreement. The disc checks your computer for existing copies of Windows XP. Press "R" when prompted to repair the existing installation.