I downgraded a PC for troubleshooting purposes to windows 8 and now it will not upgrade back to windows 10. Using the windows media creation tool to upgrade, it goes through the process and then a popup comes up saying "windows 10 installation has failed". I have tried the different files options i.e keep my files. But it made no difference. I have no third party anti-virus (some website have said that can mess with the upgrade process and cause said error). I have also tried installing it from a windows installation USB but that causes a boot loop.