I have the same problem.
When I click the "Launch" button nothing happens. So no new window etc. The console is pretty much the same as the one in this thread.
System: Win7 64bit, java 8u45 (just updated to 51 again and it works), FTB launcher 1.4.7.
I have tried deleting the FTB launcher config folder, reinstalling the launcher, force updating the mod and using other versions of Java (8u51, 8u45 7u80, 7u79). Nothing worked.
I have tested Direwolf20 1.7.10 v 1.5.0 and 1.6.1. Other mods seem to have the same issue, eg. FTB Infinity. Not all mods have that problem: Material Energy^4 eg. works.
After I have tested something on my Laptop with the 1.4.1 version I switched over to my main system that had 1.5.0 and it was not working. Both were pretty much the same build though (win7 x64, jre 8u45,...) so I would say it's the mod pack and not the launcher, because after the downgrade to 1.4.1 my main system works again...
@ jrjack3124: You can try downgrading it: Below the big line at the top (News, Options,...) there is a smaller one (Filter Setting, Edit Mod Packs, ...). Click on the one that says "Recommended" and select "1.4.1". That will fix the used version to 1.4.1. If it asks you if you want to downgrade the version hit yes.
If you have not played with modpack version 1.5+ yet, you shouldn't be afraid of loosing any blocks or corrupting your world. Let us know if it helped you!
