1.
Try running the following command at the command prompt (as an administrator) :
SFC/SCANNOW
2.
Fix a failed SQL Server installation from the installation center

start the SQL Server installer (setup.exe) from the SQL Server installation media. After prerequisites and system validation, setup will display the SQL Server Installation Center page. Click Maintenance in the left navigation area, and then click Repair to start the repair operation.

If the installation center is started using the Start menu, the location of the installation media needs to be provided at this point.
Setup support rules and file routines will run to ensure that your system has the required software installed and that your computer has passed setup validation rules. Click OK or Install to continue. On the Select Instances page, select the instance that you want to fix, and then click Next to continue. The maintenance rules will run to verify the operation. To continue, click Next. The Ready to Fix page indicates that the operation is ready to proceed. To continue, click Fix. The fix progress page shows the status of the fix operation. The Finish page indicates that the action is complete.

Fix a failed INSTALLATION of SQL Server using the command prompt
Run the following command at the command prompt: setup.exe/Q /ACTION=Repair /INSTANCENAME= INSTANCENAME
3.
https://support.microsoft.com/en-gb/help/969052/how-to-restore-the-missing-windows-installer-cache-files-and-resolve-p?Wa = wsignin1.0