Tried many things to fix, some of which included reinstalling PD, moving to various sys restore points, system diagnosis etc.
Looks like the prob may have been with the GPU driver (NVIDIA GTX580). Used the Device Manager's Roll Back driver feature numerous times in conjuntion with GPU driver uninstall.
Reinstalled the latest GPU driver minimally - haven't used PD extensively yet but looks very promising.
Wanted to post a quick note as I've been banging my head on this for days, and hopefully this helps others who may have the same/similar issue.