I have this issue intermittently with my CoD - after playing for some time and exiting the game to return to windows I am presented with a white screen outline of Steam and an unresponsive PC. Have tried killing various processes to no avail.
My machine:i7-2600 Quad Core (3.40GHz, 8MB Cache)
ASUS® MAXIMUS IV EXTREME-Z: INTEL Z68 ROG MOTHERBOARD
16GB KINGSTON HYPER-X GENESIS DUAL-DDR3 1600MHz, X.M.P (4 x 4GB
2GB AMD RADEON™ HD6950 - 2 DVI,HDMI,2 mDP - DX® 11
120GB INTEL® 320 SERIES SSD, SATA 3 Gb/s