A reboot loop (or boot loop) occurs when a Windows device unexpectedly restarts at some point during its otherwise normal startup process. Reboot loop behavior indicates an important computer problem that effectively puts the computer into a closed loop that cannot allow the system to finish a complete, stable boot cycle.
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System reboots or restarts are perfectly normal when a machine is first powered on or is restarted to complete the installation of an update, a patch or other system hardware and software changes. Only a single boot process should be needed to initialize system hardware, hand off boot control from the firmware (BIOS) to the operating system and perform a complete boot of the OS.
A boot process includes a myriad of different "handshakes" to detect hardware, load drivers and perform countless other steps between the Windows Startup icon and the desktop. In a properly configured and functional computer, those handshakes occur without incident, and the system successfully completes its boot cycle to the Start screen or desktop environment.
But an error or unexpected response encountered during a boot step can cause the boot process to restart in an effort to clear the problem. Windows simply tries to boot again -- leading to a continuous loop.
Many issues can potentially cause a Windows reboot loop, but almost all situations involve an error introduced unexpectedly in the aftermath of a hardware or software change. This means a reboot loop can usually be corrected by understanding and undoing any changes.
For example, reboot loops may occur after you make a change to the system firmware settings, install new drivers or a Windows Update, inadvertently launch malware from an infected download, email an attachment or URL or even install a new role in Windows Server.
Firmware changes are easy to correct: Re-enter the system's Setup in the moments after a reboot, revert any changes, and then allow the system to restart. As the boot process hands off to Windows, try starting Windows in safe mode.
If the system performs a stable boot to safe mode, it is usually possible to run a complete malware scan and use System Restore or other repair tools (depending on your Windows version) to undo any updates or software installations that might have preceded the reboot loop. Keep in mind that some repair or restoration processes may require Windows installation or user-generated repair media.