......how do I check?
IMO, you already have checked. You have pretty much covered all the software related trouble shooting that can be done.
As the device is not detected at all, it seem`s to me that it is not getting power. So as far as the OS and related software is concerned it does not exist. This points directly to the power switch as the next logical culprit.
If the PC is still under warranty I would be on the phone to them.
One other thing you can attempt. Normally the NIC is a replaceable part. It can be accessed through one of a couple removable panels on the underside of the lap top. The proper panel is only held in place by one or two screws. When you find the right one the NIC can be positively identified by one black and one white wire connected to it. While I do not think this is the problem, you can try gently re-seating it.
It is pretty much horizontal. One edge of it is in a mini-pci slot. Two, opposite edges, are held in place by metal spring clips. You can gently push down and towards the mini-pci slot on the fourth, open edge, ensuring it is completely seated. If you should choose to totally remove it. First
unplug the power cord and remove the battery. Purely a precaution. Then after taking note of the proper terminals for the black and white wire connections they can be gently pulled off of their posts. Carefully slightly spread the metal clips and pull out the NIC. Then reverse the procedure to replace it. Being sure it is seated fully in the mini-pci slot as well as the clips. Reconnect the wires to their proper posts.
Replace the battery, plug in the cord, start it up. IF
we are lucky it will work.