Does windows startup repair fix broken, corrupt system files regardless of the situation.

It is the correct tool, in the first instance, to use to fix corrupted system files.

How to use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7, or Windows 8.
http://support.microsoft.com/kb/929833

See "Cannot repair member file file details".

"This entry indicates that the file content does not match the operating system definition for the file. In this situation, the SFC.exe program cannot repair the file."

How to analyze the log file entries that the Microsoft Windows Resource Checker (SFC.exe) program generates in Windows Vista
http://support.microsoft.com/kb/928228#appliesto

See "Step2: If the System File Checker tool cannot repair a file."

Use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7
http://support.microsoft.com/kb/929833

If the System File Checker fails these options come into play. 

Most new machines come with a recovery partition allowing you to go back to the time of purchase, you will have to check your user guides (or the manufacturer's Web Site) for instructions.  Choosing that path requires you to save all valuable data first.

These options are built-in to Windows 8 also.

How to restore, refresh, or reset your PC
http://windows.microsoft.com/en-US/windows-8/restore-refresh-reset-pc

One way of not losing data is to make Backups of valuable data.