Safe mode is a satisfactory fallback for systems that become unbootable because a device driver crashes during the boot sequence, but in some situations a safe-mode boot won’t help the system boot. For example, if a driver that prevents the system from booting is a member of a Safe group, safe-mode boots will fail. Another example of a situation in which safe mode won’t help the system boot is when a third-party driver, such as a virus scanner driver, that loads at the boot prevents the system from booting. (Boot-start drivers load whether or not the system is in safe mode.) Other situations in which safe-mode boots will fail are when a system module or critical device driver file that is part of a safe-mode configuration becomes corrupt or when the system drive’s Master Boot Record (MBR) is damaged.
You can get around these problems by using the Windows Recovery Environment. The Windows Recovery Environment provides an assortment of tools and automated repair technologies to automatically fix the most common startup problems. It includes five main tools:
• Startup Repair An automated tool that detects the most common Windows startup problems and automatically attempts to repair them.
• System Restore Allows restoring to a previous restore point in cases in which you cannot boot the Windows installation to do so, even in safe mode.
• Complete PC Restore Called ASR (Automated System Recovery) in previous versions of Windows, this restores a Windows installation from a complete backup, not just a system restore point, which may not contain all damaged files and lost data.
• Windows Memory Diagnostic Tool Performs memory diagnostic tests that check for signs of faulty RAM. Faulty RAM can be the reason for random kernel and application crashes and erratic system behavior.
• Command Prompt For cases where troubleshooting or repair requires manual intervention (such as copying files from another drive or manipulating the BCD), you can use the command prompt to have a full Windows shell that can launch any Windows program—unlike the Recovery Console on earlier versions of Windows, which only supported a limited set of specialized commands.
When you boot a system from the Windows CD or boot disks, Windows Setup gives you the choice of installing Windows or repairing an existing installation. If you choose to repair an installation, the system displays a dialog box called System Recovery Options.
Some OEMs install WinRE to a recovery partition on their systems. On these systems, you can access WinRE by using the F8 option to access advanced boot options during Bootmgr execution. If you see an option Repair Your Computer, your machine has a local hard disk copy. By following the instructions at the Microsoft WinRE blog (http://blogs.msdn.com/winre) you can also install WinRE on the hard disk yourself from your Windows installation media and Windows Automated Installation Kit (AIK). Additionally, if your system failed to boot as the result of damaged files or any other reason that Winload can understand, it instructs Bootmgr to automatically start WinRE at the next reboot cycle. Instead of the dialog box, the recovery environment will automatically launch the Startup Repair tool. At the end of the scan and repair cycle, the tool will automatically attempt to fix any damage found, including replacing system files from the installation media. You can click the details link to see information about the damage that was fixed. For example, the Startup Repair tool fixed a damaged boot sector. If the Startup Repair tool cannot automatically fix the damage, or if you cancel the operation, you’ll get a chance to try other methods and the System Recovery Options dialog box will be displayed.
Source of Information : Microsoft Press Windows Internals 5th Edition