Hi there guys,
I believe I am hitting the same problem. I was playing fine yesterday and this morning when I came to do my "usual-Saturday-routine" the software (doesn't matter if it is from Steam or clicking directly to the Rocksmith2014.exe) won't start and it doesn't say anything it just goes back from 'Stop" to "Green-Play" btn (or if you run the .exe you won't see anything at all).
I have uninstalled/re-installed, restart but nothing, the only way to make it run is to remove the D3DX9_42.dll from the Rosksmith folder...
I see from the post above that there was an update, was it a Steam update or a Rocksmith one? I am asking cause if it's the latter I am wondering if we can go back to the previous one.