I come to the party rather late on this one but I spotted the discussion having had the "files won't open" issue on my Win8.1 PS CS6 machine today. In the end it dawned on me that, being an avid "startup process tidyer", I'd recently disabled three processes namely:
NVIDIA Capture Server Proxy
NVIDIA NvTmru Application
SwitchBoard Server (Adobe)
As soon as I re-enabled these my Photoshop functionality came back. Not sure which of the above was responsible but maybe something to check if you run into the same problem.