Getting this message: Invalid Partition Table! after I ran a Windows Update downloads and install. My laptop is looping in start up. Not able to press F(, because the function is not activated. Anyway, I am not able to make a repair. The only thing I'm able to run is the DOS-promt. And I can find this OS drive (C:\). I tested the SSHD with succes.

How did this happen? And how to solve this problem without a reinstall of Windows?

Do you have a Windows 8.1 media or a bootable USB drive?If then you can repair Start up/MBR.

Insert the Windows 8 Installation Disc in your systems optical drive/a bootable USB

Select Repair option.

Choose Troubleshoot > Advanced.

From Advanced option,launch Command Prompt.

bootrec.exe /fixmbr
Reboot after the completion of the above command.