Cause 1: A device driver or a recently installed software or service is stopping Windows from booting up normally. There has been a corruption in the Windows registry.
Solution 1a: Restart the computer and log into XP in Safe Mode. Open Device Manager and look for any problematic devices. Ensure that any jumper settings on the hardware are properly set. If the hardware is properly configured and you are still facing the problem, then it may mean that the device driver for the hardware needs to be updated. Remove the device through Device Manager and reboot normally. Obtain the updated device drivers for the hardware (through the Internet, a CD, etc.). Run the Add Hardware Wizard and reinstall the device drivers.
Solution 1b: Reboot the computer in Safe Mode. If the problem is not related to hardware, or you don’t see any problematic devices in Device Manager, run the System Restore utility to roll back the computer to a previous time when you know it was working normally.
Solution 1c: If System Restore doesn’t get your computer to start normally, get to the Windows Advanced Options menu and select “Last Known Good Configuration (your most recent settings that worked)”. Windows XP will start the computer using the Registry information from the last shutdown.
Solution 1d: If the Last Known Good Configuration does not work, then your final course of action is to do an in-place upgrade. Run the Windows XP Setup program from your installation CD. Refer to the Upgrading Windows XP from Windows 98 section of this guide. The steps are similar.
Solution 1e: If you suspect that a recently installed system service is causing this problem, stop the service by following the steps outlined earlier.
Cause 2: The BIOS settings are incorrect.
Solution 2: Restart the computer and enter the BIOS setup screen. If you have changed any settings, restore them to the previous values. If you are not sure about the previous values or haven’t changed the settings, select the Load Fail-safe Defaults (this could also be “Factory Defaults”, “BIOS Setup Defaults”, etc.) option and reboot.
Cause 3: There might be a hard disk failure or data corruption in the boot records
Solution 3: Insert the Windows XP installation CD and restart the computer. On the “Welcome to Setup” screen, press [R] to start the Recovery Console. You will be prompted for the administrator password. Type in the password, or if the password is blank, hit [Enter]. At the command prompt, type in “chkdsk”. This will run the Checkdisk utility that will scan the hard disk for any faults. Checkdisk may report a hardware failure or errors on your disk. If it does, it is best to take your PC to a repair professional.