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My co-worker came to me with his Dell Inspiron 35xxx laptop (Haswell i3).  Windows 10.  He said the other day the Wifi just turned off and he couldn't figure out how to get it working.  There is no physical WiFi switch, you can toggle airplane mode on/off using Fn+F2.  He later plugged the laptop in via ethernet, which worked fine for a couple days, then that too stopped working.

I brought it home last night figuring it was an easy fix.  So I uninstalled all network drivers and reinstalled them and found some odd things:
1) Even after installing the ethernet driver, no ethernet device shows up in the network adapters list or device manager.  Can't get internet connection via ethernet.
2) WiFi still stays off regardless of Fn+F2 toggles or flipping the WiFi "switch" in Windows 10 settings.  Flipping the WiFi switch in Windows 10 settings shows wifi seemingly turning on (initiating), then after a few seconds the switch just moves itself back to the off position.  The Wifi device shows in network adapters, but nothing I could think to try would get it to turn on.  There is a greyed out wifi icon in the taskbar with a red X saying something to the effect of "Not Connected, No WiFi signal"

I'm kinda stumped.  My typical approach in these situations is to reformat.  But I figured I'd check with the gerbil collective for any other device before taking these extreme measures.

Did you get the drivers from Dell? A lot of times they do crap to them to only work with specific stuff in their machines.

I've been given one of these today to look at too, didn't get around to it yet.
Probably coincidence, but rollback the driver or grab older drivers off the NIC manufacturer directly in case it's a recent Intel/Realtek windows update cockup!

Assuming it's not a hardware or driver fault since it seems to have affected the wired LAN port too, one thing I've seen that's often overlooked is malware.

I've seen malware try to install a snooper virtual adapter or network client and tunnel all traffic through that, intercepting packets or redirecting traffic maliciously. It'll get cleaned up and deleted by anti-malware and any other software defences, but the damage it does to the registry, drivers and network stack often remains afterwards, even if there's no immediate evidence of the attack. In that case, uninstall all the things you can from the connections (Microsoft client, F&P sharing, QoS, LL Topology etc) and then uninstall the adapter from device manager, removing the driver package as you do so. Once that's done for both WAN and LAN connections, reboot and then install manufacturer's drivers and hope for the best.

I can't think of a good reason for it to have been activated, but in some Dell laptops you can turn off networking stuff in the BIOS. Looking might not hurt

I've had good results using the repair tool from the command line in windows 10

I downloaded the WiFi and LAN drivers from Dell.  I feel like chances are slim that BOTH driver releases are fubar?  Even if the physical ethernet jack was broken, shouldn't the LAN driver still install and show up on the network adapters list?

Chrispy_ wrote:

uninstall the adapter from device manager

I did actually do this first.  When I was looking in the device manager,  the Realtek(?) 1705 wifi adapter was there, but there were also quite a few network adapters that didn't look familiar, so I figured it was best to just delete them all.  Then, when I ran each driver executable, I first selected the uninstall option to make sure everything was gone, then I installed each driver.

The thought of malware had crossed my mind.  Unfortunately, my co-worker had Norton AND McAfee installed.  I didn't know which one he actively used and didn't want to accidentally activate the other also.  I personally don't like either program.  However, it was past midnight when I got to the point of virus scans and I didn't feel like grabbing Avast install media on a flash drive and running it.  Might try that before reformatting though, thanks!

I gave the machine back to him today and told him to back up anything he didn't want to lose because my next steps had the potential to be a bit more...drastic.

As usual, to rule out hardware problems you can boot some other OS from a LiveCD, like Ubuntu.

meerkt wrote:

As usual, to rule out hardware problems you can boot some other OS from a LiveCD, like Ubuntu.

This++.  Now that you've eliminated the easy software troubleshooting, confirm the hardware and/or BIOS has not been borked before getting into the advanced brain damage.  If the unit doesn't have an optical drive you'll either need to obtain a USB optical drive or else create a bootable Ubuntu flash drive.

Could be related to this story: https://tech.slashdot.org/story/16/12/10/014231/new-bug-in-windows-10-anniversary-update-brings-wi-fi-disconnects

Have you checked msconfig/services.msc to make sure the network related services haven't been disabled?

So, to update - mine was a 169.254 APIPA address and was fixed with a simple netsh int ip reset command.
It seems that the Windows update cockup has affected millions!

A little update on Ars: http://arstechnica.com/business/2016/12/microsoft-windows-10-dhcp-broken-update/

Thanks for the suggestions!! I'll be trying these in a few days and report back.

DPete27 wrote:

I wasn't able to find much with a google search but it seems awful convenient that this corruption is in the NetworkService directory when I'm having networking issues.  Any suggestions on how to fix this?  I'm fresh out.  Tried deleting aforementioned file and nothing changed.

With it deleted you can always try the SFC /scannow to check, but given that is a temp folder I don't expect it to be critical to the functioning of the network stack. 

Did you try meerkt's suggestion of booting a live distro and seeing if that worked? Because it sounds like a hardware issue or a corrupted OS at this point, and booting to another OS would quickly rule one of those out. 

Went straight for the jugular and did a clean install of Windows 10.  All problems still persist.  Going to try buying a USB WiFi stick.  I figure that ought to bypass any problems that are happening on the mobo.  USB ports are working fine.