To run the Windows Vista System File Checker in safe mode:
Open the 'start' menu. Type 'cmd' in the search bar, do NOT press ENTER. Right click on the 'cmd' executable file in the search results and choose 'run as administrator'.
When the administrative window opens, type the following:
SFC /scan now and press ENTER. Windows Vista will begin checking all essential system files and making repairs when necessary. This may take quite a while, and you may be required to insert your Windows Vista installation disk.