Upgraded the firmware yesterday after a chat with @OzoneVibe from .700 to 4.0100 and now when I plug the MP into the PC it makes the noises as before but doesn’t show it as a drive anymore.
I’ve tried various USB ports and different combinations of putting the cable in the PC or MP first and turning on before or after and nothing works.
When Windows 10 upgraded back last year it stopped seeing cards in the card reader, it still has that issue as I’ve tried all I can find on the internet about that, Now I have this.
The way I got around it for this mornings photos was to put the card in the Spark and take them that way.
Any ideas on what the problem might be?
Also the MP is more stable than when I had it on .700 but it takes ages to connect to Go4 and occasionally shuts the feed off, I’m thinking that might be the cable though.
Did DUMLdore confirm the updated version OK?
I have to admit, I don’t think I’ve ever connected MP to computer to retrieve files.
I always use a USB 3.0 card reader.
Sounds like it might be a driver issue though.
Like @callum - I almost never attach mine as a drive. Files copy quicker from the SD card in the laptop, and I spend enough tome recharging batteries without wasting them for file transfers. 
But, for some reason I connected mine, the other day, and (I think!) the drive only appeared when I had DJI Assitant running.
See if you can see it then.
Edit: Just remembered … I was wanting to access flight logs … and you need to connect DJI Assistant for that.
Yes, I followed the video and confirmed it was on the .4.0100
I always used to remove the card and transfer that way until the card reader issue, the laptop went exactly the same when it updated Windows 10 as well 
Then it CAN see the MP … just not the card as a drive.
Either, as @callum says, drivers. Uninstall DJI Assistant and then reinstall.
Or, since you cannot see other SD Cards, there may be a bigger issue with your Win10 installation.
Have you tried connecting to a different computer?
As for Go4 losing the feed - I’d agree that it’s probably the cable.
Just tried that and still nothing 
Yes, the laptop went the same after the same update.
Can you try a computer that you’ve …. errrrr …. Win10 hasn’t blown up?
Never heard of a computer not seeing SD card drives. A strange one.
I’ve just built one for my daughter and her partner, I didn’t think of giving that a try.
When I tried looking for an answer on the internet it was quite a common fault, I tried all what these so called experts with a video camera were telling me but still nothing.
I think I’ll pack it in for today and have another go tomorrow maybe, or I may just stick the card in the Spark for tonight.
Also, check if the MP drive is visible in Disk Management.
You say it makes the noises, so it’s getting so far in making the connection.
I did have an issue like that when I added an extra HDD, it didn’t show and I had to alter some things, I can’t remember how I did that now.
Thanks for the help, I’ll let you know how I get on.
I’ll be offline most of the next 3 days … at Goodwood Festival of Speed.
I’ll try and log in and see how things are progressing.
Just started up Disc Management and it wasn’t showing, powered the MP back on and it flashes up in there, the MP then makes the noises as well as the PC and file explorer pops up showing the DCIM from the MP.
Very strange.
Thanks for your help, lets hope that has fixed the issue, if not I know what to do to get it to show now at least.
Some progress! 
Need to get the SD card reader working … life’s too short to use the slow route.
Started Disc Management as Dave mentioned and the DCIM file pops up as it should in file explorer, If it’s not fixed at least I now know what to do next time.
Thanks guys.
Yes
You can help me with that another day 
Thanks again
Checked mine out of curiosity.
Does not show as a mass storage device and like yours makes all the correct noises.
Checked drivers installed correctly. Deleted drivers and let windows install defaults, still no joy.
Used Zadig tool, and Windows is detecting it as a storage device. Tried all available drivers, winusb, libusb etc but does not show as a storage drive.
Windows panel on LHS sort of moves when you plug in mavic as if an extra folder layer has been added but nothing is there.
Looks like a bug of some sort.
Not an issue for me as I use external sd card reader but just thought I’d try it out of curiosity.
Out of curiosity, open Disk Management like Dave mentioned and then power it up, What does it do then?