Check the displacement map value.  If it looks high, it will choke your render.  You may need to rely on bump mapping but it will affect the hair appearance on closeup.  On your render, apply a value to the min. displacement bounds (i.e., 0.1), it may not be necessary but when you hover over that setting, the help field below recommends increasing the value from zero. 

Otherwise, uncheck Use displacement maps and rerender.  This might narrow down the problem.