Blender 2.72b was rendering animation overnight. Windows updated and restarted computer. In morning on relaunching the .blend file by double clicking the file opened, but any attempt to interact with it causes the window to announce (Not responding)
Launching blender.exe works and can load other files but not the one that had been running that night, nor, suprisingly, the immediately preceding version of the .blend file. Both had been fine yesterday.
There seems to be something in those last two .blend files that for some reason after the interruption is causing the freeze.
(This is after a similar problem which I solved by removing the username/config/userpreference file in appdata. The .exe had been freezing if launched directly.
Worked if launched from a double clicked project.blend file.
Deleting the userpreference file in appdata solved that.)
Tested with v2.72b and v2.73
W7 pro 64bit
Cuadro k2000