Missing operating system: Windows 7

After starting my PC today, I was staring at a little message on my screen: Missing operating system. At first I was a little bit shocked, but of course I knew that this only means that either my disk has some small disk errors or my master boot record  is damaged.


Unfortunately, the solution is not 42, so let’s find out what we can do about it!

Run chkdsk to repair disk errors

First of all, don’t panic! If you panic and do things without thinking about consequences, you might damage your system and lose data. The solution to this problem is usually very simple. Your hard drive might have disk errors, therefore you are not able to start your system. This often happens when you restart your PC during a boot-up secquence while it’s loading safe-mode for example.

1. Find your Windows 7 DVD.
2. Start your PC, insert your Windows 7 DVD and hit a key when you are asked to (to boot from DVD). It is possible that you have to change the boot order in your BIOS to boot from DVD.
3. Follow the instructions on the screen, but don’t install Windows 7, instead click on “Repair your computer“:

The installer will now search for Windows installations on your PC and list them all. Select your Windows 7 installation and click on next.


4. Open the command prompt.

Attention: Do NOT click on “System Restore” or “System Image Recovery”. If you try to restore/recover your system that way, you might damage your Windows 7 installation irreversibly.
5.You will probably be in a folder X:\sources\ . Don’t worry, if your partitions are still there you can run a chkdsk on them.

Run a chkdsk for your main partition (e.g. C:), to do that enter:
chkdsk c: /f/r

/f /r will both fix errors and recover lost data.
/f will only fix errors on your disk
/r will only recover lost data

This will, in most cases, repair your disk errors and you will be able to start Windows 7 again.

Windows 7 Bootrec.exe – Repair MBR

While you’re at it, you also might want to repair and fix your MBR (Master Boot Record), add a new boot sector and scan your disk for Windows 7 installations.
/fixmbr
This will create a new Master Boot Record, but will not overwrite your exisiting partition table.
/fixboot
This will add a new boot sector. If you boot sector is damaged you might not be able to start your system.
/rebuildbcd
Scans your disk for Windows-7 compatible installations, needed to repair your Windows 7 installation.