Ideally, when all the devices are configured on your computer, you should be able to work with no problems from your drivers.
Most people's computers don't remain in a static mode but are in constant flux. Even though devices are working fine, many people feel the need to try to improve performance by changing settings, upgrading drivers, or installing Service Packs.
Although upgrading drivers and installing items such as Service Packs are common practice, they should be done carefully. A Service Pack, for instance, can change how all drivers on your computer function. In the rare case when something does go wrong, you may find that the fix is difficult, but in most cases, it will be related to a file version or configuration setting.
A device referenced in system files is not found
From time to time, you will find that one of your startup files still references a device that you thought had been removed from your system. The Windows Registry holds all configuration references for installed devices. If this happens, you might have to edit the Registry manually in order to fix the problem. If an error message tells you that a referenced device does not exist, take note of the device being referenced because you will have to search for it in your startup files.If the device is listed in the Registry, as it should be nowadays, it should be listed in Device Manager. Generally, it's safer to make Registry changes through Control Panel than by using the Registry Editor directly.
Choose Start→Control Panel → System, click the Hardware tab of the resulting dialog box, and then click the Device Manager button. For Windows Vista and Windows 7, choose Start→Control Panel → System and Security → Device Manager. Locate the device in Device Manager and delete it. If the device is still physically present in the computer, it will be re-added to Device Manager when your computer is rebooted. If you keep removing the device and it keeps coming back, that is because it is still physically present. Physically remove the device first, and then remove it from Device Manager.
In Windows, if you do not see the device that you want to remove in Device Manager, choose Show Hidden Devices from the View menu. If you can't find the device in the Windows GUI, you can attempt to search the Registry to locate the device and correct the issue.
Registry corruption
The two main ways that the system Registry can become corrupted are updates to the Registry via one of the Registry editing tools or an import of a registry settings file, and by the files that make up the Registry becoming damaged or deleted.Of the many ways to import data into the Registry, most of them involve storing settings in a file and importing that file into the Registry. If the settings in the file are incorrect, you might be able to just continue computing without any problems, or you could end up with a system that no longer boots normally. If your system will not boot normally, your only option is to boot the system by using an alternative method, such as the Recovery Console, and replace the base Registry files with an untainted version.
You also need to use an alternative method to boot the system if the Registry files on the drive itself have become corrupted, and then you have to replace the Registry files. The user portion of the Registry — ntuser.dat — is found in your user profile directory. Your user profile directory is in C:\Users\<username> for Windows Vista and beyond. The system portion of the registry is found in systemroot\system32\config, in the files SAM, SECURITY, system, and software.
Safe Mode
In order to let you repair the OS from within the OS, Microsoft provides Safe Mode. Safe Mode is available with most versions of Windows and is a special boot of Windows that loads a minimal set of drivers and services. The only drivers that are loaded are the ones that are required to get the OS running. Instead of loading the normal video driver, Safe Mode loads a basic VGA graphics driver. If you have issues with drivers or driver configuration, booting into Safe Mode can allow you to bypass these driver-related problems so that they can be fixed.Safe Mode should be your "go to" boot mode when you're repairing a system that's been infected by malware. In Safe Mode you don't have Internet access because Windows hasn't loaded any network drivers; this prevents the infected system from "phoning home" and counteracting your malware removal techniques.
In Windows Vista and later, you can boot into different Safe Mode variants. For instance, you can load Safe Mode with or without networking support. Alternatively, you can skip the Windows Desktop and boot to a Safe Mode Command Prompt.
Enter Safe Mode by pressing the F8 key when the OS is booting. If your computer boots into Safe Mode, the words Safe Mode appear in each corner of your desktop. If Windows fails to boot properly, it will suggest — and attempt — to boot into Safe Mode on the next boot. If your computer boots into Safe Mode automatically, the last boot process was likely interrupted (usually by the user).
