Did the modpack crash? or did it give you some error?
Please tell me about it and give me the crash/error message and what you were doing while it happened, that way I can fix it.
If the error message is really long you can put it on pastebin.com and give me the link.
If the modpack is running slow on your computer you can try to install fastcraft to it. Fastcraft is a mod that makes minecraft much faster for most people. FastCraft