Windows – Lenovo T420 integrated camera is not working

First thing: Check BIOS

F12 on boot... System Configuration > Miscellaneous Devices > Enable Camera.

I have 35 of the the 13" ones. The commenters are correct that it is not normal for it to disable in device manager. I just got powershell to sweep the office DELL's:

• 15 listed the webcam as "imaging device".
• 20 listed as "Integrated Webcam".
• none disabled.

In fact, a quick visual shows that 4 users have a post-it stuck over it, so there maybe not be hardware/software key to disable it either... I usually re-format the DELLs to vanilla Windows 10 as soon as they hit my desk - all functions work... it will install as "Integrated Webcam" instead:

You have done most of the right steps to check/resolve so far but I will re-iterate them here

1. Ensure winver is 1709 There was an issue just before Windows 12-month anniversary update called "webcam-gate" that blocked many 3rd party webcams. This shouldn't affect you as you are using the generic imaging-device drivers... but it's a no brainer to do the latest Windows 10 update anyway. The Creator's Update (v1709) solves a few other issues with "Exclusive mode" (where 1 app takes control of a device and no others can see it) so ensure you are up-to-date first.

2. Dell's PC diagnostics on boot (F12) After the first set of tests (~7 minutes) you can say "no" to additional RAM tests... and then be presented with a results screen. It will indicate if Webcam was skipped or tested. please confirm.

3. Check events for that driver Back in Windows, open device manager +x or right-click start and select "device manager"... double-click your device in question... choose tab "Events". You are looking for events where it started happening. Maybe a power event, or an insufficient resources clash. (you will need to scroll through a bunch of "device install requested" events from your recent tests.

4. (Software Option) eat fresh Uninstall it, (deleting the drivers) and try and get it to install usbvideo.inf_amd64_06d8dbf36a7321ac. This will make it pick up as a webcam, rather than imaging device. Failing that: Fresh install of Windows 10 by using the Windows 10 Media Creation Tool. The only thing from DELL you probably need is the DELL Update tool - and maybe DELL Software Delivery, if you want it to put that bloatware back on there (There are better free options, DELL just gets paid to shovel that onto your PC, which in turn keeps your purchase cost down... that's the only reason it's there). You don't need help+support. That is just a re-badged version of software called "PC-Doctor" and it allegedly causes issues with some PC-Security vendors (can provide sources if asked).

4. (Hardware Option) Check connectivity as per comments This one takes a bit of guts, but it might be a fix (maybe you want to do software options first):

• Check USB Connector for Webcam

Before you start this - know that you WILL lose the magnets that help hold the lid closed. They are held in by hot-snot and will flick out easily. You can pop them back in loose, or just chuck them out. Flip over the PC undo the 10 screws on the backplate and pop it off, disconnect the battery and hold the power-button on the laptop to drain any residual electricity within. The internal USB ports are tiny. The webcam is top-right corner from memory. but just check those 2-3 ribbon cables are clipped in snug. The wide one is Video, the tiny one is webcam, and the medium one (~5mm wide) is the Windows button. If you have a touchscreen model I think it terminates there too.

• Pop open the screen.

See that ugly rubber seal running the edge of the screen? Stick a spudger (or plastic knife/wedge) between that and the plastic shell and pop it off carefully. Workshop manual says to un-bolt the 4 hinge-anchors within the actual chassis first... but if you call them they say don't bother. just click that case off and check the cable running up to the webcam is still OK, and connected at both ends.