During an upgrade to Windows 10 the process hung at the "Checking for updates" stage.
This is quite a common problem, here is how I got around it.
Once process has hung:
Do Start - All Programs - Accessories.
Right click on Command Prompt
Select "Run as Administrator".
When prompt appears, type
net stop wuauserv
net start wuauserv
The update should then proceed. Hopefully.