RebeccaVenter, WIN10 can make it more challenging vs WIN7 as a reboot will not necessarily clear these PD running processes. I've seen reboots of WIN10 launch them again on boot as it was when the reboot was commanded. In fact, that is a feature of WIN10 to "bookmark" running processes and attempt to restart them on reboot or shutdown. That's why some WIN updates return the open app state as it was prior to the update.
If it's still occurring after a reboot, add the column "Image path names" to the Details tab of Task Manager. Sort by path and do a screen capture of the section covering the path name area of:
C:\Program Files (x86)\CyberLink
and
C:\Program Files\CyberLink
Post the pic and I'd think something will probably stick out as the culprit and then you can manually kill that tasks.
The concurrent user session is usually aggravated when user has shutdown PD and instantly try to relaunch or PD has crashed during an edition session or user terminated. If PD had been working previously, and now won't launch anymore and nothing else has changed more often than not a service of PD is still running. Often but not always it's PDHanumanSvr.exe. A laptop in hybernate mode when the cover is closed can also cause such issue.
Jeff