Couple updates -- the restarts are caused by a DRIVER_POWER_STATE_FAILURE error -- there is a BSOD after all I just wasn't around to see it. The dump files identify the problem as pci.sys. Bug check code is ..0x9f. From poking around on forums closest I can come to figuring this out is that it may be the NVIDIA Geforce 900 driver (i have a 960 card installed), but I updated to latest version (358.50) and problem still persists. Still looking for ideas ... thx.