A system file check may be able to reinstate the firewall which is done by going Start Orb > type
cmd.exe > right click on
cmd and select Run as administrator > accept the UAC > type
sfc /scannow at the prompt and press enter to see what that reports.
You can also go Start Orb > type
services.msc > press enter and check that the Base Filtering Engine, RPC (RPCSS) and Windows Firewall services are showing as Started and Automatic then go into Device Manager/View/Show hidden devices > Non Plug and Play Drivers > scroll down to the bottom to check that Windows Firewall Authorization Driver doesn't have a yellow alert next to it - but right click on it and select Properties.
It will show if it's working properly under the General tab, but check under the Driver tab that it is set to Demand and that the Start box is greyed out which will denote it is started - otherwise click the Start button > OK.
If you have problems with the Authorization Driver then you can restore it with the batch file from
http://batcmd.com/windows/7/services/mpsdrv/ after selecting your version of Win 7 and SP1 from the dropdowns.
You could download Windows Firewall from
http://download.bleepingcomputer.com/win-services/7/MpsSvc.reg and the BFE from
http://download.bleepingcomputer.com/win-services/7/BFE.reg if required but run this ESET Services Repair Tool to see if that can get things going again
http://kb.eset.com/library/ESET/KB%20Team%20Only/Malware/ServicesRepair.exeIf you download the Firewall and BFE then you will need to go into services.msc to start them.