Maybe you don't have anything to build (and you haven't ticked "Build even if nothing has changed since the previous build"), e.g. because now all your development is done in a different branch.
If you think it's not the case, check the events logs around the time when the build should run.
Nevertheless we're off-topic here, because this has nothing to do with Dynamics AX. If needed, let's continue the discussion in a forum about Team Foundation Server.