Bottom line, concerning an unknown listed somewhere is to ascertain whether DM lists a problematic device or a software issue more than once somewhere else in the tree but really that device is currently recorded appropriately in the tree where it should have been in the first place and is appropriately installed and working. Sometimes issued occur which was caused initially by some anomaly that caused an "unknown" entry but later through tweeking and ignoring that "unknown" a user managed to set things straight elsewhere but the "unknown" entry still exists. Note that when second issues have occured -- an "unknown" and a correctly recorded entry elsewhere, it is recommended that the latter be deleted and concentration made on correcting the former -- particularly if it is hardware related. Understand however, this may be "shooting from the hip" only to see what happens -- since your guess may be as good as mine.
a. "How to Use Device Manager to Check the Status of a Resource (Q141497}."
b. "Explanation of Error Codes Generated by Device Manager (Q125174)."
c. "Troubleshooting Device Conflicts with Device Manager (Q133240)."
Followed the instructions that came with the webcam: installed drivers and software first. Then connected the webcam to the USB port: "Unknown Device" came up.
Went to Start, Control Panel, System, and found out that, there is also a problem with the video driver.
It shows: unknown PCI video device (or something like that), despite that the correct video driver is already installed.