Unable to start installation of Windows 10

• Disable all antivirus and firewalls running in your version of Windows
• Reset Windows Update by running Microsoft's FixIt tool

If that doesn't work try the System Update Readiness tool from Microsoft.

• You can also check whether Windows Update has the ability to download and install update automatically. This takes a few simple steps:

1. Open Windows Update by positioning the mouse pointer in the bottom right corner of the screen and then moving it up. After this click Settings > Change PC settings > Update and recovery.
2. Next, click on "choose how updates get installed" and on the next page choose the relevant option under Important updates.
3. From there choose "give me recommended updates the same way I receive important updates" check box from under the Recommended updates section
4. Under Microsoft Update then choose the "give me updates for other Microsoft products when I update Windows" check box and click "Apply."
5. Open up Windows Explorer to view the files on your PC. Go to C:\Windows\SoftwareDistribution\Download and delete all the files that are in the folder (but don't delete the folder itself).

When you've done all of that, launch the Command Prompt in Administrator mode (you can do this by pressing the Windows Key on your keyboard and X, then select "Command Prompt (Admin)" from the menu that appears) and type in: wuauclt.exe/updatenow. Your download should then begin and you'll be able to enjoy Windows 10.

If after all of this you're still unable to run the update, you can create media (ISO) with Microsoft and then run the installation. It is very simple, click here to check how.