Hi,
I had the same issue as a lot of people the you would launch the FTB exe and nothing would happen, in the task manager java would open and close again.
I ran the .jar version of FTB in CMD and found it couldn't find the locale folder.
The local folder should be located:
Win7/8/Vista
C:\Users\<Username>\Appdata\Roaming\ftblauncher
XP (I have not checked this as I dont run XP, have a hunt for it)
C:\Documents and Settings\<Username>\Local Settings\ftblauncher
Anyway for may solution I found just a .zip called locales.zip in this folder, I simply unzipped this to locales and then removed the "s" from the "locales" folder so it was now "locale"
After this all was well
Hope this works for all you people.