rem open a cmd prompt
rem run the following
rem this will re-install the firewall
rem WAIT for a minute for the process to complete - it will NOT look like it is doing anything
rem Did you WAIT!!!
rem
rem reboot when complete

c:
cd \windows\inf
rundll32 setupapi,InstallHinfSection Ndi-Steelhead 132 netrass.inf




Windows 7 update - from http://www.gandalf.net/firewall
this will hopefully help you not to have to reinstall your OS if your windows 7 firewall stops working due to an attack from malware or virus

Windows firewall service is missing or will not start
 If it will not start with Error 1075, The dependency service does not exist or has been marked for deletion skip this and get your Base filter Engine working (see below)

if your windows firewall service is missing and you do not have the entry in your registry ((Regedit hkey_local_machine/currentcontrolset/services/MpsSvs) get a copy of MpsSvs Key from any other windows 7 computer
 export it and then import it into your registry
 You will need to fix permissions on the entry!
 Add full permissions to Local Service & Network to the Registry Key

Base filter Engine missing or will not start with permissions issue

IF your BFE entry is missing (Regedit hkey_local_machine/currentcontrolset/services/BFE) get a copy of BFE Key from any other windows 7 computer
 export it and then import it into your registry

You will need to fix permissions on the entry!

Browse to the location for the BFE service in the registry
 (HKLM\System\CurrentControlSet\Services\BFE\), right click and select permissions.
 2. In the "Permissions for Policy" window, click advanced | Add.
 3. Once the "Select Users, Computers or Group" box appears, change the "From this location:" to point to the local machine name.
 4. After changing the search location, enter "NT Service\BFE" in the "Enter the object name to select" box and click "Check names" - this will allow you to add the
 BFE account.
 5. Give the Full privileges to the BFE account:

Reboot.