ive had this strange PXE issue since first installing SCCM 2012, everytime the server was restarted, the WDS service stayed in a "starting" state until i mucked about with turning pxe off and on again on the DP.
today, i changed the the WDS service startup type to "Delayed start", and after a couple of reboots, pxe and wds work correctly
i'm hoping this works for other people