If your modpack doesn't start make sure you've assigned it at least 3 GB of RAM or else it won't start!
I don't recommend using OptiFine, because it often causes render issues and even crashes!
Please note that most of the mods updated for 1.10.x are still in beta or even alpha and can be buggy sometimes. If your world gets corrupted you can try to rescue it with MCEdit (http://www.mcedit-unified.net/)
If this doesn't work, please send an e-mail with the crash-log to [email protected]