I have been experienced this issue. Only splash screen appeared and then it will show as 'Not Responding' in the Task Manager.
Solution :
1. Uninstall Tera from Gameforge Launcher
2. Uninstall Gameforge Launcher
3. Delete any files/folders in relation to Gameforge/Tera on your PC (some of them is inside the %AppData% folder and Program Files x86)
4. Clean using CCleaner
5. Restart your PC
6. Reinstall Gameforge Client & Tera Online
7. Exclude Tera folder from your Antivirus (example Windows Defender Exception)
8. Profit