Missing operating system
Cause:
The MBR (Master Boot Record) has an invalid partition boot entry so the operating system can not be launched. This issue occurs prior to the start of any Windows code.
It can be caused by a power-failure while the disk is in the middle of writing, a virus damaged the entry or a serious software bug damaged the partition entry (although Windows typically protects against this). This issue cannot be easily caused by any action you performed, unless you turned off the power without going through Windows shutdown.
Although not stated in the message, press Ctrl-Alt-Del to reboot.
Workaround:
1. Change Boot Media
If you are booting from either a DVD, CD, diskette or a USB drive, remove the media and boot from the hard disk. The media is either damaged or is not intended to be bootable.
2. Set the Correct BIOS Boot Choice
The BIOS may be configured to boot from the wrong device. If you suspect this, the device boot order can be changed in the BIOS setup. Be aware there little consistency in BIOS setup operations, even with the same manufacturer on different models. As such, these instructions are bit less precise than we'd prefer.
1. Reboot and enter the BIOS setup. Often the BIOS displays the correct key to use briefly on screen or you may need to refer to the computer's user manual. Typically you hold down the Del, Esc, F1 or F2 key immediately after booting.
2. Look for a section on Boot or Booting. Often this appears on top menu. Select the Boot option, and if necessary the Boot order choice. The Boot order choices should list the order of boot devices. Typically the CD is the first boot device with the hard-disk typically second. The diskette may also occur before the hard disk, which is acceptable, although this will slow your hard disk boot by a few seconds. Avoid USB and network boots before the hard disk unless you know for sure you are using them (which is exceptionally rare).
Save and exit the BIOS. It will force a reboot. See if this change corrects the issue.
3. Fix the Partition Boot Record
Windows provides tools to install a new partition boot record. Doing this does not erase any operating system files or your personal data. If this is the only damage, it has a good chance of fixing the problem, but if additional system sectors are damaged, recovery will be very difficult if not impossible.
1. To reset the Windows boot sector, boot from your Windows installation CD/DVD.
2. Go into the 7/Vista Recovery Console or XP Recovery Console and select Command prompt.
Description of the Windows XP Recovery Console.
How to use the Command Prompt from Windows Vista Recovery Environment?
Validate and Fix the File System
This runs the check disk program to detect and attempt to repair problems on one partition. For example, to repair the C: drive:
At the prompt type chkdsk c: /r
Repair the Boot Process
Windows XP:
Typically this is used if Windows doesn't start at all and you can't get to the safe mode menu. You might also replace the Master Boot Record (MBR) and/or the boot sector if you suspect a virus infection.
New MBR - Insert a new generic MBR without changing the partition table.
- At the prompt, type: fixmbr
New Boot Sector - Insert a new Windows compatible boot sector.
- At the prompt, type: fixboot
- It will confirm the target partition is C (for at least 99.99% of installations). Type Y
Vista/ Windows 7
Typically this is used if Windows doesn't start and you can't get to the safe mode menu. You might also replace the Master Boot Record (MBR) and boot sector if you suspect a virus infection. There are four options:
New MBR - Insert a new generic MBR without changing the partition table.
At the prompt, type: bootrec /FixMbr
New Boot Sector - Insert a new Windows 7/Vista compatible boot sector. It will automatically insert the right type of sector for the file system type (NTFS, FAT32, etc.)
At the prompt, type: bootrec /FixBoot
Rebuild BCD - Rebuild the Boot Configuration Data (BCD). The BCD controls which partition boots. This option will let you select which installations to include in the BCD.
At the prompt, type: bootrec /RebuildBcd
Find OSes - Scan the system for all OS installations that are compatible with Vista/2008 and will also show those that are currently included in the BCD.
At the prompt, type: bootrec /ScanOs
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