Update, maybe relevant for other users: xFast USB seems to be the troublemaker! It's an Asrock programme that, if I interpret it correctly, is designed to speed up data transfers. I just restarted my pc again, after that the Helix and I got a blue bsod (with lots of text in white letters). Yesterday I didn't get any blue sod's, i just got a black screen and then an immediate restart. So maybe the windows updates cause this difference.
Anyway; after that, I restarted the pc (Helix off), then closed the xFast program (it autostarts), thén turned on the Helix: no problems.
Conclusion of the day: let's uninstall xFast :)
I hope it is solved now. And that this topic is helpful for users experiencing similar issues.
Thanks again, time to rock :)
Jeroen