1. Reboot the computer. While Windows is trying to boot, continuously press the 'F8' key. A screen of various mode options. Choose to boot Windows in 'Last Good Config' or 'Safe Mode.' 'Last Good Config' is the better choice, but Windows may not be able to boot in that mode. You will need one of these modes to access your CD-ROM.
2. Put in your Windows CD in the CD-ROM after Windows have loaded in one of the above modes.

3. Reinstall and repair Windows using the Windows Installation disk. The setup screen will appear automatically after you put the CD in. Click on 'Reinstall Windows' on the setup screen. Follow the installation wizard to repair Windows to a state that can load without errors.
4. Restart Windows after the installation. The mode screen may appear again. This time choose 'Start Windows Normally' to start Windows as you would before the errors started. You shouldn't have any other problems loading Windows now.