XPS 15 7590 Touchpad not working - driver issue

I had the intermittent problems as described in https://www.dell.com/community/XPS/XPS-15-TouchPad-ClickPad-Intermittent-Problems-Possible/td-p/7762060/page/3, therefore I applied the solution on Page 1 (unchecking "allow computer to turn off this device to save power"). This lead to the touchpad not working anymore at all in Windows - in BIOS it works just fine so the hardware is okay. 

I therefore applied the solution on Page 3 (re-installing Intel Serial IO IC2 Host Controller A368 and A369). This changed just one thing: The touchpad is now also working on the Windows logon Screen. As soon as I actually logged on, the touchpad is not working anymore. I also tried the newer driver from the last post - same result.

Does anybody have an idea what else I could try? I would really appreciate it!