EE reported: FCT belt had stopped, he was kneeling along side the machine's computer screen attempting to determine the mechanical problem. A piece of draw rock (14"" x 19"" x 2""-3"" thick) fell from between roof bolts striking the top of his head, sliding down his upper back & falling to the mine floor. The area was bolted with resin bolts using 14"" aluminum pie pans on each bolt.