Not having many options I kept my troubleshooting simple. A bit of research showed others with similar issues but not my EXACT issue. The resulting error after the failure was always “ The installation failed in SAFE_OS phase with an error during INSTALL RECOVERY ENVIRONMENT operation OxC1900101-ox20004“. It tried loading from the desktop as well as USB. Each attempt to install the Windows 10 upgrade failed at 25% and 84% copying files. My install of Windows 8.1 was clean except for Microsoft Office 365 and Firefox. So I spent a few hours struggling to install the Windows 10 upgrade on my Windows 8.1 professional computer. The installation failed in SAFE_OS phase with an error during INSTALL_RECOVERY_ENVIRONMENT operation OxC1900101-ox20004 The installation failed in SAFE_OS phase with an error during INSTALL RECOVERY ENVIRONMENT operation OxC1900101-ox20004
