Because troubleshooting system problems is a complex process, and hardware and software configurations can vary greatly, there are many approaches you can take to fixing problems that might prevent Windows from starting (booting) correctly. Here are some tools you can use and strategies you can try:
System Restore can return your system files to a point in time before you noticed a problem, without affecting documents, photos, or other personal files. If System Restore doesn't fix the problem, you can undo the restore operation and choose another restore point. For more information, see What is System Restore?
Memory. Memory errors might be caused by faulty random access memory (RAM). To scan your computer's memory for errors, see How do I know if my computer has a memory problem?
Hard disk problems can be caused by corrupted system files or by physical errors on the disk itself. To scan your computer's hard disk for errors, see Check your hard disk for errors.
Devices and drivers. If you installed a new device, video card, or other hardware item that is causing problems, the driver for the device might be incompatible with Windows. For more information, see Tips for fixing common driver problems. If uninstalling or restoring the driver back to a previous version does not fix the problem, try uninstalling or removing the hardware, and then restarting your computer.
Compatibility. Most programs written for Windows XP also work in this version of Windows, but some older programs might run poorly or not at all. If a program written for an earlier version of Windows doesn't run correctly, use the Program Compatibility Wizard to change the compatibility settings for the program, or use the program's Compatibility tab to change the settings manually. For more information, see Make older programs run in this version of Windows.
Uninstalling. If you cannot uninstall the program, try using System Restore to restore your system to a point in time when it worked correctly. For more information, see What is System Restore?
System Restore. System Restore can return your system files to a point in time before you noticed a problem. System Restore works without affecting documents, photos, or other personal files. For more information, see What is System Restore?
Multiboot order. If you have more than one operating system installed on your computer (a multiboot configuration), you can choose which one starts when you turn on your computer. For more information, see Change the default operating system for startup (multiboot).
Safe mode. You can use safe mode to temporarily disable programs that start themselves when Windows starts. If one of these programs is causing a problem, you can start your computer in safe mode and then uninstall the program before it starts. For more information about safe mode, see Advanced startup options (including safe mode).
If your computer will only start in safe mode, recently installed hardware or programs might be causing the problem. Try uninstalling recent programs or recent hardware and see if that fixes the problem. For more information, see Troubleshooting problems while in safe mode.
Startup Repair. Startup Repair is a Windows recovery tool that can fix certain problems, such as missing or damaged system files, that might prevent Windows from starting. Startup Repair is located on the System Recovery Options menu, which is on the Windows Vista installation disc. If your computer has preinstalled recovery options, it might also be stored on your computer's hard disk. For more information, see Startup Repair: frequently asked questions and What are the system recovery options in Windows Vista?
If your computer does not include Startup Repair, your computer manufacturer might have customized or replaced the tool. Check the information that came with your computer or go to the manufacturer's website.
Change restart settings in safe mode. If your computer is stuck in a loop where Windows fails, attempts to restart, and then fails again repeatedly, restart your computer in safe mode and select the Disable automatic restart on system failure checkbox. For more information, see Advanced startup options (including safe mode).
Reinstall. If no other options have solved the problem, and you are sure that your computer's hardware is functioning normally, you might need to reinstall Windows. A custom (clean) installation of Windows will permanently delete all of the files on your computer and reinstall Windows, so only use this option if all other recovery options have been unsuccessful. After the installation, you will need to reinstall your programs and restore your files from backup copies. For more information, see Installing and reinstalling Windows.
For general troubleshooting, including information about e-mail, networking, using the web, and hardware drivers, see Troubleshooting in Windows. For information about Windows installation and activation, see Installing Windows: frequently asked questions and Activating Windows: frequently asked questions.