Sometimes the following happens:
Device Manager
We don't know which device is "unknown" - it's not clear.
You can try to set the location of the driver as follows
C:\Windows\System32\drivers (don't forget to tick Show compatible hardware), it
might have some effect. But what if this doesn't work? Stay calm, because we
have a solution even if everything fails:
1. In the context menu Unknown device, select Properties.
2. Go to the tab Details and select Hardware Ids from the drop down list.
Device Properties
3. There you can see lines like PCI\VEN_10EC&DEV_8168&SUBSYS_81681019&REV_01
4. Write down 4 characters after VEN_ and DEV_. In this case, 10EC and 8168,
respectively.
5. Go to the website http://pcidatabase.com/ and input those characters into one
of the fields Vendor Search orDevice Search (preferred).
PCI Vendor and Device Lists
6. Finally
Device Search Results
That's it, now search the driver for your OS and install it.