Whats the exact error message that you get when you try to turn on firewall? If the error message is "firewall settings cannot be changed at this time" then it might be firewall driver issue. All you need to do for this is you need to open "Microsoft windows onecare live" folder in program files. In here you will find a folder called "FIREWALL". Open firewall and inside that you may find two folders. Open the first folder and right click the second file present in there and click on install. After that open the second folder and right click the second file present in there and click on install.
After this restart your computer once.
Open command prompt by start-->run-->cmd and in here type net stop winss and later type net start winss.. Mostly your firewall problem might be fixed. *******************************************Good luck **************************************************
