[1.7.10] Troubleshooting

If your game crashes or does not start, we do NEED a crashreport

Without a log file or at at least a extensive description of your problem, we can do absolutely nothing to help you.
So please follow the following steps (If you have questions about the steps themselves, feel free to ask):

1. Find the Minecraft log file If you use the standard Minecraft launcher, the interesting logfile is .minecraft/logs/fml-client-latest.txt. (How to find the .minecraft folder). In case you have a server, the interesting log file should be logs/fml-server-latest.txt. If you use another launcher, it might have a function to easily upload or locate log files.
2. Make a post in the Minecraft Forum thread, describe the problem and include the log either within a spoiler or as a Pastebin of it. If you know what you are doing, you can also create an issue on Github.

Example of a good crash report here

Besides that there are two things which can make stuff easier for you or us:

1. MultiMc is a very useful launcher/mod manager, which allows you to upload your log files with one click.
2. OpenEye is a useful mod, which sends crashes together with some useful information to the mod authors, so please consider installing this.