start-control panel-system-hardware-device manager
If you see any “YELLOW QUESTION MARKS”..
YOU are missing drivers!
(bet a wooden nickel its the ethernet controller driver)
Modem driver and VGA driver
go to dell.com/downloads and support put in your model number (EXample dell sx260) and look for the driver in the network tab/box..download it through your browser and install...
The plug and play only works for the PCI slots. The Ethernet is built into the board as are the video and sound. I am typing on one that I upgraded a month ago and had to put a Ethernet card in it to get on the net so I could get the Compaq drivers for the board. They had them, and everything was up to date.
We have a winner for the most helpful post. Clear, well written.