Sometimes, a service goes down for a time. Maintenance, high traffic . . . . . . Just try again later.

What happens if you try looking for Firefox from the programs list on the start menu instead of from the Desktop icons ?

Or from the Run command ? On Windows 7 pressing the Windows Key + R should get a run command line up. Enter firefox.exe does that start Firefox.

If it has been uninstalled follow these instructions to reinstall it

• How to install Firefox on Windows

As long as you did not use some third party uninstaller Firefox should have retained its settings bookmarks and password. It should do no harm attempting to install Firefox again.

Did you try to reboot the computer (possibly in Windows Safe mode)?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

You can do a disk check with the chkdsk.exe program.

If you run the chkdsk.exe program from a cmd.exe Command window then you can read the response from the chkdsk.exe program. Open a cmd.exe window:

Start > Run: cmd.exe <press Enter>

At the command prompt (>) type or Copy&Paste: chkdsk.exe /f /r <press Enter> (put a space before /f and /r) If you get something like: Would you like to schedule this volume to be checked the next time the system restarts? y/n then answer the question with "Y" and close all programs and reboot the computer.