Windows Vista : Recovering Systems (part 2) - Dealing with startup instability

11/17/2012 1:05:03 AM

2. Level 2: Dealing with startup instability

Level 1 problems deal with system instability issues. In this case, the system starts up, but operates in an erratic manner. As you have seen, there are lots of tools that support the correction of these types of issues. Level 2 deals with startup instability or issues related to configuration or other changes that affect how a system starts up. Windows Vista includes several tools that support the repair of a system at system startup. They include two main tools:

  • Last Known Good Configuration

  • Safe Mode Startup

Both of these tools have been in Windows since its very earliest editions.

Using Last Known Good Configuration

Last Known Good Configuration (LKGC) is a startup option that relies on registry settings that were in use the last time the computer startup up successfully. LKGC has been around since the days of Windows NT. It was the only option you could rely on to correct startup instability issues.

Each time you make a significant configuration change, such as installing a new device driver or adding an application, this change modifies both the file system and the system registry. Each time you make significant changes to a system, Windows writes the existing configuration into a subset of the registry. Each time the system successfully starts, however, Windows replaces the content of the LKGC with the current boot settings. As you can see, the data in the LKGC is volatile and must be used as soon as you discover an issue otherwise it may no longer be valid.

If Windows detects that the system did not start properly, it will automatically display the LKGC at the next startup. If it doesn't and you want to access it, then you must press the F8 key repeatedly as the system is booting and before the Windows Vista logo appears. If the logo appears, then you are too late and must recycle the system once again. After Windows detects the F8 key, it will provide you with an advanced startup screen that displays the LKGC option (shown in Figure 11). To boot into the LKGC, simply select it and press Enter. The system starts with the data contained within this special registry store.

Most commonly, administrators relied on the LKGC to repair systems after installing video drivers that would not work with their installation of Windows. In this particular case, the LKGC would very rarely provide a solution and administrators needed to rely on other methods to repair the system. Although Microsoft did improve LKGC with time, you should still consider it a last resort and should only be used if nothing else works. Using LKGC can leave the system in an unstable state and should really only be used if for some reason there is unsaved data within the system and you cannot re-image it with a new OS installation until you recover this data.

Figure 11. Using F8 to access Advanced Startup options

Using Safe Mode startup

Another powerful startup option is Safe Mode. Windows includes three different safe mode startups:

  • Safe Mode that starts Windows with only core drivers and services

  • Safe Mode with Networking that uses only core drivers, but also includes networking

  • Safe Mode with Command Prompt that uses only core drivers and automatically launches the command prompt

You usually rely on Safe Mode Startup when you face an issue with a newly installed driver that you cannot get to work. For example, if you installed a new video driver and your system does not respond correctly to this new driver, you can start Windows in Safe Mode to try to replace the video driver.


You can also use the Enable low-resolution video (640×480) to specifically repair video driver issues. This option starts Windows normally with all drivers and services, but runs it in low-resolution mode.

Safe Mode is useful for dealing with issues, such as needing to disable a device driver, return a driver to its previous version, or even launch a System Restore to return to a specific restore point. Safe Mode gives you access to the full Windows interface but without loading the more complex drivers your system may rely on.

Disabling a device is the easiest, but of course you wouldn't disable the video driver, so it has limited value. Disabling devices is done in the Device Manager. Use the following procedure:

  1. Use F8 to start the system in Safe Mode and log in after the system is started.

  2. Once in Windows, launch Device Manager. Use Control Panel => System and Maintenance => Device Manager and accept the UAC prompt.

  3. In Device Manager, locate the problematic device. If the device is causing known problems in Vista, it will be displayed with a question mark beside it. If not, then expand the Tree pane until you see the device.

  4. Right-click on the device and select the appropriate action (see Figure 12). You can Update Driver Software if you have a new driver on hand, uninstall the device, or simply disable it.

  5. Reboot the system in normal mode.

You can also rely on Safe Mode and Device Manager to restore a device driver to its previous version. Use the same procedure mentioned previously, but this time, select the device's Properties. In Properties, move to the Driver tab and click on Roll Back Driver (see Figure 13). Windows displays a warning; click Yes. After the driver is rolled back, reboot the system into normal mode.

Finally, using System Restore in Safe Mode is the same as using it in normal mode. If System Restore can resolve the problem, then this might indeed be the best tool to use.

Figure 12. Using Device Manager in Safe Mode to disable a driver

Figure 13. Rolling back a device driver
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