You can press Shift+F10 to open the command prompt during the
startup repair and can run that command.
I assume that you have the Windows-7 bootable disk. So then its very easy to get back you system working again. Before this enter to bios setup and check that your default boot device is CD/DVD drive, if it is not then set it to your default boot device. Follow the steps given below:
1: Insert the Windows 7 installation disc and restart the PC and press any key when prompted.
2: Select your language preferences and click on Next. Click on Repair your computer.
3: Select which operating system you want to restore and the click on Next.
NOTE: If Windows 7 is not listed here, or it is blank, then it is ok. Click on Next anyway.
4: Select the system recovery option you want to do.
Here you have to select the Command Prompt and then run that command. You can also try the
Bootrec /fixmbr and
Bootrec /fixboot to fix the problem.
If that doesn't help then you can try few more things as I have found it on seveforum. Just follow these steps after entering in Command Prompt
1: On Command Line acessed the folder with the files that should substitute
C:\Windows\System32\Config. To do that, type cd windows, then cd system32, then cd config
2: Type 'dir' to see the files. There were 5 files with the termination .gbck, and 5 files without any termination. They are the following files: DEFAULT, SAM, SECURITY, SOFTWARE and SYSTEM.
3: Rename all the files without termination to .bak one by one. just like that: ren COMPONENTS COMPONENTS.bak (you should do it for the others 4 files)
4: Rename all the .gbck to without termination one by one. just like that: ren COMPONENTS.gbck COMPONENTS (you should do it for the others 4 files)
5: Type dir, to see if the files names were exactly you are expecting to.
6 Restart the PC.