Reinstall the WinCC as follow:
* uninstall the WinCC and the MS SQL Server under "Settings --> Software"
* delete in the Registry under "HKEY_LOCAL_MACHINE --> SOFTWARE --> SIEMENS" the folder "WinCC"
* delete in the Registry under "CURRENT_USER --> SOFTWARE --> SIEMENS" the folder "WinCC"
* delete under "C:\ProgramFiles\Siemens\" the folder "WinCC"
* reboot the computer and install the MS SQL Server and the WinCC again