Actually I have two problems and couldn't find a fix anywhere.
1. When I hit play it starts loading, but when it's finished the launcher just flashes and it doesn't open the game
2. I can't download some Modpacks. It says it's downloading, but the loading bar stays at 0%. I tried deleting the files manually from .technic, but now it only brings up an Error message with no useful information in it when I try to redownload modpacks.
I really tried fixing it myself a lot, which brings up another problem: My Log is around 2000 KB, making it too big for Pastebin aswell as Ubuntu. Does it help if I only upload it partially?