I came across a problem when Upgrading from Windows 7 to Windows 10 RS2.
Essentially the install was stuck on the "Welcome to Windows 10!" screen. Once Next was clicked nothing happened. I could continue moving the mouse but couldn't do anything else:
I had to remove the MediaTek RT2860 802.11n USB Wireless LAN Card and then hold down the power button to switch the PC off. (In other systems switching off the WiFi/BT switch should also work and remove all unnecessary USB peripherals). I then waited 30 s to power back up the computer. This allowed me to finish the installation as normal.
Adding the MediaTek RT2860 Wireless USB 802.11n dongle post installation when the computer was logged in made the wireless networks take forever to load:
When the computer was powered up with the MediaTek RT2860 Wireless USB 802.11n dongle installed a black screen showed, with the taskbar (which eventually disappeared). Again I could move my mouse but the taskbar didn't respond:
The issue is the driver which is detrimentally interacting with the Windows shell. There are somehow more issues with Wireless/Bluetooth drivers for these kind of things.
Again adding the MediaTek RT2860 Wireless USB 802.11n dongle post installation when the computer was logged in tets look at the driver first. Right click the start button and select Device Manager:
Expand Network Adapters:
Look for the 802.11n USB Wireless LAN card (or your Wireless Card) right click it and select properties:
Select the driver tab: 
Then look at the driver version. In my case when I tried to Uninstall Device here it failed:
So I had to press [Windows] and [ r ] and type in msconfig and press [Ok]:
Then go to the Boot tab:
Enable Safe Boot and then select Apply:
Then select Ok:
Then select Restart:
Then in safe mode select close at the this App can't open message:
Right click the start button and select Device Manager:
Expand Network Adapters:
Right click the 802.11n USB Wireless LAN Card and select Uninstall Device:
Ensure Delete the Driver Software for this Device is checked (otherwise it'll reinstall the Device with the faulty driver restoring your problem). Repeat this for any Bluetooth devices listed:
Now that the Device is gone we can now leave safe mode and let Windows reinstall the driver itself (from its inbuilt drivers):
To leave safe mode press [Windows] and [ r ] and type in msconfig and press [Ok]:
Go to the Boot Tab:
Uncheck Safe Boot and select Apply: 
Select Ok:
Select Restart:
You should now be logged in normally and have no issues even though the WIreless USB Device is attached. Right click the start button and select Device Manager:
Right click the 802.11n USB Wireless LAN Card and select properties:
Select the Driver tab:
You can see the driver version is older but this doesn't matter as long as the card works:
I can go to wireless networks and they can load as normal: 
