It happens from time to time. The firewall service just fails to start!
What might be the problem and what might fix the problem?
In this blog post, Nitin shows you one reason why this would happen and how you can fix it.
Check it out at:
http://blogs.msdn.com/b/nitinsingh/archive/2013/06/03/microsoft-firewall-service-wspsrv-exe-on-forefront-tmg-threat-management-gateway-is-not-starting.aspx