Twitch Launcher

Update Java with the Twitch Launcher
When you start up the pack with the twitch launcher, it will normally use an old Java version (1.8.0.25) which is too old to run SevTech properly. You can change the Java version by going into 'settings' and then 'minecraft' in the twitch launcher.

Then tell it to use the JAR-launcher instead of the native launcher and then choose a newer version of java (all installed versions should appear in the list). Make sure that you have installed the correct version (32 or 64 bit). The recommended version is 1.8.0.161 or above.