If your build tells you “Build Not started”, “Waiting for an available agent”, or “Waiting for an agent to be requested”, make sure that your agent is running (if as a service, then it’s called “VSO Agent”) as well as the “Visual Studio Team Foundation Background Job Agent” service. The latter feeds the former. In my case, I am using TFS 2015 and the latter appeared to be configured as “Automatic (Delayed Start)” but had to be configured as “Automatic” instead.