you can try delete all the windows 10 partitions only while keeping Win 8.  You also need to preserve the system reserve partition on ssd if you want to be able to boot from Win 8.  Having three os installed may have caused a not so clean operating environment.  If a test install of Win 10 works, then do a complete clean install by wiping the entire ssd including system reserve partition.   when you preserve the system partition, win 10 install will not be clean as it will further modify and muck up this partition.  Even if you delete the two previous win 10 partition, the system reserve partition still has os loader for those two.  It will ask you which os to boot from even when those two win 10 os are ghost now.
Till now I used my OptiPlex 7020 MT under Windows 8.1 (x86) Pro without any problem. Now I wanted to upgrade to Windows 10 (x86) Pro. After successful installation (to a different partition) with some applications, Windows 10 freezing randomly (sometime works hours, sometime 10 minutes). Booting Windows 8.1, it is working fine. When freezing (under Windows 10), the blue screen presents a message that Watchdog VIOLATION happened. Running sfc and DISM there is no problem. All the drivers and the BIOS (A18) actualised. The PC has i3-4160 CPU, 8 GB RAM, 240 GB Patriot Burst SSD, DVD RW, 1 TB Toshiba HDD, integrated video. The BIOS set non UEFI mode. Any help can be thankfully appreciated.
Optiplex 7020 freezing randomly on Windows 10.