When a server fails to start, you need a carefully considered but fast response. Experts have some quick and easy ways to put Windows servers back on their feet, but some of these powerful techniques could render your system completely useless if you don't get them right. Generally, you should prepare for the worst case in a test environment. Admins who are familiar with the various possibilities can restore a server quickly in an emergency.

In this article, I show you how to fix problems with Windows if the operating system will not boot. The instructions have been tested with Windows Server 2012 R2, but most settings also work in previous versions and with Windows 7/8. You will learn how to restore entire servers and repair virtualized environments based on Windows, as well as how to get special services, such as Active Directory, running again.

Boot Manager Failure

If a server fails to boot, the cause can be a defective boot manager. You can repair it by booting from a Windows Server DVD and calling up the computer repair options. At the command line, you have various options for reactivating a defective boot manager.

The bootrec /fixmbr command overwrites the master boot record at the beginning of the disk, whereas bootrec /scanos lets you view the operating systems that are not currently listed in the boot manager. The bootrec /rebuildbcd command reinstates the systems found in the boot manager, and bootrec /fixboot creates the bootmgr boot manager again.

Further commands for repairing the boot manager are bootsect /nt60 SYS and bootsect /nt60 ALL. You can enter the commands in this section one after another at the command line. Of course, this is only useful if the boot manager has stopped working. If the server starts to boot but then cancels, the boot manager is not defective; the problem is with the operating system.

Windows Will Boot But Not Start

Sometimes Windows stops working or crashes after upgrading drivers. This situation applies to servers and clients. In some cases, Windows system files are destroyed so that Windows still boots, but errors appear or some features fail to launch.

In this case, you can either go back to a system restore point or call the computer repair options on the installation DVD. If you want to repair the system files on the fly, open a command prompt with administrator privileges and enter the sfc /scannow command. Windows scans important system files and restores them if problems arise.

Testing RAM and Hard Disks

Windows machines display blue screens if they discover a hardware fault in the computer (e.g., in RAM). Thus, it makes sense to test memory before trying a software repair (Figure 1). The BlueScreenView [1] tool is helpful if you need to find out the cause of blue screens. The tool does not require any installation and can be called from a USB stick.

Figure 1: Before a repair, you should test the RAM in your server.

Windows Server 2012 R2 is set up by default to restart automatically after a blue screen. If you experience a blue screen on every restart, the server ends up in a loop. The settings that define how Windows should behave after a blue screen, can be found in Control Panel | System and Security | System | Advanced System Settings .

Under Startup and Recovery, press Settings (Figure 2). First, you should disable the automatic restart. Then, under Write debugging information , choose what kind of information the operating system should save. Your best choice is Automatic memory dump or Small memory dump . BlueScreenView then parses the memory.dmp file that Windows created for the blue screens.

Figure 2: In case of blue screens, you can influence Windows start behavior in the Control Panel.

If you suspect an error on the hard disk, for example, because of clicking noises and entries in the Windows Event Viewer (Windows Logs | System ), you should test the hard disk and the filesystem. Open a the command prompt with administrative privileges and enter chkdsk /f /r. For further testing of hard disks, you can use something like the free Seatools by Seagate. The program tests most hard disks for errors – not just those manufactured by Seagate. You can find the Seatools and other information for rescuing hard disks online  [2]. Western Digital Data Lifeguard is a similar tool [3], which is also available as a Windows application. Hitachi publishes its Drive fitness tool as an ISO file [4].