Problem:
Windows no longer starts! How can I fix it?
Solution:
If Windows doesn't boot at all, you can try making it bootable again with the Recovery Console. For that, you need a clean Windows installation CD (XP or Vista depending on what you have). For Vista, there is a separate, downloadable CD image containing the Recovery Console (google for it), so that you need not buy a separate OS CD if you don't have one. Boot the recovery console from that CD, and type at the command prompt:
fixmbr
fixboot
That will rebuild the boot settings of Windows. Be aware though if you do multiple-boots with other OSes (Linux for instance): those OSes might (and probably will) become unbootable!
If Windows does try to boot, but hangs somewhere after that, try first to boot the "Last Known Good Configuration". To do that, press F8 at the initial Windows loading bar. Select "Last Known Good Configuration" and let the machine try to start Windows. If the last known good configuration doesn't work, reboot and press F8 again, then boot in safe mode and try restoring the computer to a point where it was running properly, using the Backup and Restore center (in Vista) or System Restore (in XP).
If after that Windows is still not running properly, you can try repairing the installation using the Recovery Console (get to the Recovery Console as described in the first paragraph). Please search other guides for details on the procedure.
