Error Setup couldn’t start properly. Please reboot your PC and try running Windows 10 setup again comes up when Windows installation is corrupt or a previous installation failed for some reason.
To fix this issue you will need to uninstall the previously failed installation folders and the old windows.old profile located in the C:\ Drive.
Windows.old is your old Windows; In Windows 10 you have the option to revert to previous Windows. This option is available only for a month after the windows 10 installation. So if you uninstall it; you will not be able to go back but now since you are already on Windows 10 i suggest you stick to it.
If you still wish to go back to your Old Windows; see the downgrade guide
To fix the existing issue, perform the following steps
1. Hold Windows Key and Press E
2. Open C:\ Drive
3. Show Hidden Folders
a) Click the Options button on the top right side
b) Click the View Tab
d) Click Appy/OK
4. Locate and Delete the following folders:
Now attempt the installation, it should work fine.