When a computer running Windows stops working, the first troubleshooting step is to test all of the hardware. Any failure in a critical component, including the processor, RAM, motherboard and hard drive will prevent Windows from starting. These components can be tested with individual diagnostics, or exchanged with a known good part, or relocated to a known working system.
Once the hardware components have been tested and confirmed to be working reliably, the next decision is whether to repair or erase and replace Windows.
Starting with Windows 2000, Microsoft introduced a repair feature that can be accessed from the original installation CD disc. This repair feature removes and replaces all of the Windows program files, and then rebuilds the settings used to control the operation of Windows. The Windows repair option in Windows 2000 and Windows XP is very effective, and will frequently resolve many types of software problems introduced by viruses. The repair option does not affect installed programs or user data, and does not erase the hard drive.
The Windows repair feature is also effective and useful for making hardware changes. While Windows will detect new components automatically, it will not startup if the motherboard is changed. No repair is required when changing a CPU, RAM or hard drive, although multiple changes may trigger an online re-activation request.
Prior to Windows 2000, Windows 95/98/ME/NT all lacked a repair feature. Instead, the closest choice to repair was to start in safe mode and delete all items from device manager. However, this had limited use and could not be used to resolve corrupt files and settings due to a virus. The lack of repair options in Windows 95/98/ME/NT made all of these versions of Windows unrepairable after a virus infection. Instead of repairing these versions, they can be upgraded to Windows 2000 and then repaired.
After Windows 2000/XP, subsequent versions of Windows Vista and Windows 7 introduced built-in repair features, so the installation boot disc method is no longer required. However, the repair option in Windows Vista/7 does not perform the same type of extensive repair as in Windows XP/2000, and is less effective at fixing problems due to corrupt files. It also does not effectively handle hardware changes such as a new motherboard.
Since the Windows 2000/XP repair is so effective, it is rarely necessary to erase Windows 2000/XP. However, when Windows is extensively corrupted and fails to startup or run reliably after a repair, an erase and replace approach is required. Before erasing a non-working copy of Windows 2000/XP, the best method is to backup or clone all files to a spare hard drive. The original hard drive can be replaced, and if space permits, all of the original files can be re-copied into a folder. This method ensures that all of the original files are available for recovery, while preventing any corrupt files from interfering with the new copy of Windows.