In some cases, multiple system files are deleted or become corrupt, so the repair process can involve multiple reboots and boot failures as you repair the files one by one. If you believe the system file corruption to be extensive, you should consider restoring the system from a backup image, such as one generated by Windows Vista CompletePC Backup or from a system restore point.
When you run Windows Backup (located in the System folder under Accessories on the Start menu), you can generate a CompletePC backup image, which includes all the files on the system and boot volumes, plus a floppy disk on which it stores information about the system’s disks and volumes. To restore a system from an ASR backup image, back up boot from the Windows setup media and press F2 when prompted. If you do not have a backup from which to restore, a last resort is to execute a Windows repair install: boot from the Windows setup media, and follow the wizard as if you were going to perform a new installation. The wizard will ask you whether you want to perform a repair or fresh install. When you tell it that you want to repair, Setup reinstalls all system files, leaving your application data and registry settings intact.
System Hive Corruption
• Symptoms If the System registry hive is missing or corrupted, Winload will display the
message “Windows could not start because the following file is missing or corrupt:
\WINDOWS\SYSTEM32\CONFIG\SYSTEM,” on a black screen after the BIOS POST.
• Causes The System registry hive, which contains configuration information necessary for the system to boot, has become corrupt or has been deleted.
• Resolution Boot into the Windows Recovery Environment, choose the Command Prompt option, and then execute the chkdsk command. If the problem is not corrected, obtain a backup of the System registry hive. Windows makes copies of the registry hives every 12 hours (keeping the immediately previous copy with a .OLD extension) in a folder called \Windows\System32\Config\RegBack, so copy the file named System to
If System Restore is enabled, you can often obtain a more recent backup of the registry hives, including the System hive; from the most recent restore point. You can choose System Restore from the Windows Recovery Environment to restore your registry from the last restore point.
Post–Splash Screen Crash or Hang
• Symptoms Problems that occur after the Windows splash screen displays, the desktop appears, or you log on fall into this category and can appear as a blue screen crash or a hang, where the entire system is frozen or the mouse cursor tracks the mouse but the system is otherwise unresponsive.
• Causes These problems are almost always a result of a bug in a device driver, but they can sometimes be the result of corruption of a registry hive other than the System hive.
• Resolution You can take several steps to try and correct the problem. The first thing you should try is the last known good configuration. Last known good (LKG), consists of the registry control set that was last used to boot the system successfully. Because a control set includes core system configuration and the device driver and services registration database, using a version that does not reflect changes or newly installed drivers or services might avoid the source of the problem. You access last known good by pressing the F8 key early in the boot process to access the same menu from which you can boot into safe mode.
When you boot into LKG, the system saves the control set that you are avoiding and labels it as the failed control set. You can leverage the failed control set in cases where LKG makes a system bootable to determine what was causing the system to fail to boot by exporting the contents of the current control set of the successful boot and the failed control set to .reg files. You do this by using the Regedit’s export functionality, which you access under the File menu:
1. Run Regedit, and select HKLM\SYSTEM\CurrentControlSet.
2. Select Export from the File menu, and save to a file named good.reg.
3. Open HKLM\SYSTEM\Select, read the value of Failed, and select the subkey named HKLM\SYSTEM\ControlXXX, where XXX is the value of Failed.
4. Export the contents of the control set to bad.reg.
5. Use WordPad (which is found under Accessories on the Start menu) to globally replace all instances of CurrentControlSet in good.reg with ControlSet.
6. Use WordPad to change all instances of ControlXXX (replacing XXX with the value of the Failed control set) in bad.reg with ControlSet.
7. Run Windiff from the Support Tools, and compare the two files.
The differences between a failed control set and a good one can be numerous, so you should focus your examination on changes beneath the Control subkey as well as under the Parameters subkeys of drivers and services registered in the Services subkey. Ignore changes made to Enum subkeys of driver registry keys in the Services branch of the control set.
If the problem you’re experiencing is caused by a driver or service that was present on the system since before the last successful boot, LKG will not make the system bootable. Similarly, if a problematic configuration setting changed outside the control set or was made before the last successful boot, LKG will not help. In those cases, the next option to try is safe mode (described earlier in this section). If the system boots successfully in safe mode and you know that particular driver was causing the normal boot to fail, you can disable the driver by using the Device Manager (accessible from the Hardware tab of the System Control Panel item). To do so, select the driver in question and choose Disable from the Action menu. If you recently updated the driver, and believe that the update introduced a bug, you can choose to roll back the driver to its previous version instead, also with the Device Manager. To restore a driver to its previous version, double-click on the device to open its Properties dialog box and click Roll Back Driver on the Driver tab.
On systems with System Restore enabled, an option when LKG fails is to roll back all system state (as defined by System Restore) to a previous point in time. Safe mode detects the existence of restore points, and when they are present it will ask you whether you want to log on to the installation to perform a manual diagnosis and repair or launch the System Restore Wizard. Using System Restore to make a system bootable again is attractive when you know the cause of a problem and want the repair to be automatic or when you don’t know the cause but do not want to invest time to determine the cause.
If System Restore is not an option or you want to determine the cause of a crash during the normal boot and the system boots successfully in safe mode, attempt to obtain a boot log from the unsuccessful boot by pressing F8 to access the special boot menu and choosing the boot logging option. Session Manager (\Windows\System32\Smss.exe) saves a log of the boot that includes a record of device drivers that the system loaded and chose not to load to \Windows\ntbtlog.txt, so you’ll obtain a boot log if the crash or hang occurs after Session Manager initializes. When you reboot into safe mode, the system appends new entries to the existing boot log. Extract the portions of the log file that refer to the failed attempt and safe-mode boots into separate files. Strip out lines that contain the text “Did not load driver”, and then compare them with a text comparison tool such as Windiff. One by one, disable the drivers that loaded during the normal boot but not in the safe-mode boot until the system boots successfully again. (Then reenable the drivers that were not responsible for the problem.)
If you cannot obtain a boot log from the normal boot (for instance, because the system is crashing before Session Manager initializes), if the system also crashes during the safe mode boot, or if a comparison of boot logs from the normal and safe-mode boots do not reveal any significant differences (for example, when the driver that’s crashing the normal boot starts after Session Manager initializes), the next tool to try is the Driver Verifier combined with crash dump analysis.
Source of Information : Microsoft Press Windows Internals 5th Edition
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