Blank screen after repair

One of my friends has a Windows 7 computer, but suddenly it could not start, and he asked me for help

I got an error like this
File: \Boot\BCD
Status: 0xc0000098
Info: The Windows Boot Configuration Data file does not contain a valid OS entry

And I ran a

Code:

chkdsk c: /f /r

followed by a

Code:

Bootrec /RebuildBcd

, where it asked me, if I want to add the entry to the BCD store, and of course I answered yes

Afterwards I rebooted the computer, but it came up with a blank screen.
I then tried to restart the computer and it keeps coming up with a blank screen. I tried to repair using the Windows 7 - cd's repair, but with no succes. It found the Windows 7 Home Professionel, but when I tried to repair it, it says, that it could not find the OS (something like noOSInstalled). I then came into cmd again, and tried first with

Code:

BootRec

, but it could not find the OS.
Now I set it to run

Code:

chkdsk

over the night, but what can I do, if I comes up with the blank screen again?
Do I have to reinstall the computer, or are there other solutions?

CHKDSK found ad sectors in the following files

Code:

\Windows\assembly\NATIVE~1.303\PRESEN~1\FFB7C7~1\PRESEN~1.DLL
\Windows\assembly\NATIVE~2.303\SYSTEM~3.SER\559EBA~1\SYSTEM~1.DLL

If this indicates something

Maybe I have to try with F8, when I restarts the computer for the first time after running the

Code:

BootRec

. Could that be a solution?