Why do startup problems happen?

Windows may fail to start for a variety of reasons, and generally speaking in order of decreasing likelihood here they are:

• Hardware failure
• Bad driver
• Corrupt file or volume
• System misconfiguration
• Virus infection

Here is where we need to apply our brains and use a bit of common sense to determine what the cause of startup failure might be. Think of the previous list above as a list of disease-causing viruses, and now you have to play doctor and figure out which virus the patient (your sick computer) actually might have. For if you skip this step and try blasting the patient with every possible remedy in your doctor's bag, two things may happen:

• One of the remedies you try may actually make the patient worse and indeed could prove fatal.
• You'll waste a lot of time and the recovery of your patient will be delayed, and your boss may get upset with you as a result since her business is losing money due to downtime.

So careful diagnosis is a step you should always take time for and never avoid, and just like in the medical profession such diagnosis usually begins with your senses. For example, do you smell something burning? Better unplug your system immediately and wait for things to cool off, then open the case and inspect the damage. Do you hear your CPU fan making a slow grinding sound? Power down your system and replace the fan before your processor burns out and needs replacing. Is your video display flickering? Maybe try reseating the video card after checking if the video cable is seated properly.

Let's assume its not such a simple and obvious problem. Instead, say you get a black screen with one of the following dreaded messages when you try and boot your system:

• "NTLDR is missing"
• "A disk read error occurred"
• "Invalid partition table"
• "Error loading operating system"
• "Could not read from selected boot disk"
• "Windows could not start because the following file is missing or corrupt"

Or you might get a blue screen (called a STOP screen) with some obscure message on it. Or if you're lucky you might make it all the way through the Windows splash screen to the logon box and then suddenly get a dialog box saying "One or more services failed to start". Or your mouse pointer might freeze and your system hang either before or immediately after logon. How can you match these symptoms to the underlying condition that might be causing them? First let's look at some possible "black screen" messages that can occur after the BIOS POST routine finishes but before the Windows splash screen appears:

Symptom	Probable Cause
"Invalid Partition Table" "Missing Operating System" "Invalid Partition Table"	Master boot record is corrupt due to hard disk errors or virus infection
"NTLDR is missing" "A disk read error occurred" System hangs after BIOS POST finishes	Boot sector is corrupt due to hard disk errors or virus infection
"Windows could not start because of a computer disk hardware configuration problem" "Could not read from selected boot disk" "Check boot path and disk hardware"	Boot.ini file is corrupt, missing, or needs updating.
"Windows could not start because the following file is missing or corrupt"	Boot volume is corrupt or the referenced system file is missing.

In addition to these error messages, a variety of other startup problems can occur including:

• Blue screens. These are typically caused by hardware failure or driver problems but can also be due to virus infection.
• Hung system. These are typically caused by buggy drivers or by registry corruption but can also be due to virus infection.
• Dialog box saying "One or more services failed to start". This is typically caused by misconfiguration or registry corruption but can also be caused by application incompatibility of some form.

In a nutshell, here's a quick inventory of the main tools:

• Last known good. Restores the HKLM\System\CurrentControlSet portion of the registry its version during the last successful logon to the system.
• Safe mode. Starts Windows with a minimal set of drivers and creates a record of which drivers load in %windir%\Ntbtlog.txt.
• System Restore. Windows XP only feature to restore system to previously saved configuration.
• Recovery Console. Boots to a command line that allows you to run various commands.
• Automated System Recovery (ASR). Restores the boot volume from backup.
• Repair. Run Windows Setup from your product CD and select the option to try and repair your installation.

Which tool should you use to address each of the symptoms we described earlier? Assuming there is no obvious hardware problem (no funny smell) and you've already asked yourself the Golden Question ("What was the last thing I did to this system?") then here's a quick outline that maps the type of knife (may be several in order of severity) to the kind of surgery (underlying problem or visible symptom) you need to perform on your system:

Problem/Symptom	Tool(s) to Use
Corrupt master boot record	Recovery Console (fixmbr)
Corrupt boot sector	Recovery Console (fixboot)
Corrupt or missing boot.ini	Recovery Console (bootcfg /rebuild)
Corrupt system file	Recovery Console (chkdsk) Restore from ASR backup Perform a Repair install
Corrupt registry	Recovery Console (chkdsk) System Restore (XP only) Restore system state from backup Perform a Repair install
Blue screen	See this resource first Last known good System Restore (XP only) Safe mode (roll back suspect driver using Device Manager)
Hung system	Last known good System Restore (XP only) Safe mode (roll back suspect driver using Device Manager)
"One or more services failed to start"	Don't logon! Reboot and select last known good, log on, undo the last configuration steps you performed. Safe mode (undo last configuration steps you performed)