I'm having the same issue. it started as hit and miss, and now is consisitent with all modpacks I try to run. It started this week. After the Technic launcher window closes, during the modpack boot up, sometimes the minecraft window with the forge boot up progress doesn't open. I check my task manager details and see that Javaw.exe is still running and taking up RAM, but no window is opens. I can't <end process> or <end process tree> the javaw.exe it remains persistant and hug, even after user log-out and log-in. Trying to start another game through the launcher gets the same result. the hung java persists until a computer reboot.
Let me know what application and log information you want. For now attached is the technic log for today: https://pastebin.com/6x4nN1pF
Windows 10 64bit
Java 1.8.0_161
NVIDIA's latest drivers for GForce GT 730
I've tried uninstalling and reinstalling java, technic, modpack. I've turned off CCleaner, Malwarbytes, Windows defender.
I'll try rolling back GeForce 391.24 Game Ready Driver, maybe this post relates: https://forums.geforce.com/default/topic/1040875/-official-391-24-game-ready-whql-display-driver-feedback-thread-released-3-20-18-/?offset=28
Thanks!
Best,
Charles