Try this: *Download the Firefox installer and save the file to the desktop<br>https://www.mozilla.org/en-US/firefox/all/ *Start the installation with a double-click on the desktop icon ---- Did you check your security software? Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) to see if that helps. *http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/ *http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10