Sality is the thing that integrates its function automatically to .exe and .scr file and causes files to corrupt. It is spread by catching to running exe file and slowly causes all files to corrupt. It is also the downloader which downloads malicious files from the web and it reduces internet speed and has a firewall which blocks antivirus websites.
To remove sality from your PC you have to download Kaspersky Salitykiller or AVG Sality Removal Tool which helps to remove Sality infected files and to unblock Anti Virus Website.
To Reinstall corrupted Windows files use Run Command sfc /scannow; it may require Windows CD to restore Files.