Windows Defender

After a bout with ZeroAccess and win32:serefef-pl my computer was left with no firewall. I cleaned the offenders using Roguekiller and repaired windows firewall using Repair_windows as advised in another post. I have since discovered that windows defender also does not work, it is there MSASCui.exe in its rightfull folder but fails to initialize 0x8007006 when clicked on. I have scanned my computer using all the tools as advised.