[NAME]  Please press the blue Accept as Solution button below if this answers your question. You will have to reset F2 bios to default and boot windows You Must switch F2 BIOS SATA OPERATION  to AHCI not RAID or IRRT IRST. from within windows after boot. Secure boot should be OFF F2 Bios Security tab to install ubuntu alongside windows 10. Windows 10 will need to be changed from RAID to AHCI first. Switch operation from either IDE / RAID to AHCI  within Windows 10 without having to reinstall.  Here are the steps: Click the Start Button and type cmdRight-click the result and select Run as administratorType this command and press ENTER:  bcdedit /set safeboot minimal Restart the computer  It will boot windows with black desktop background. Restart again and go into F2 bios and change IRST RAID to AHCI Change the SATA Operation mode to AHCI  from either IDE or RAID Save changes and exit Setup and Windows will automatically boot to Safe Mode. Right-click the Windows Start Menu.  Choose Command Prompt (Admin). Type this command and press ENTER:  bcdedit /deletevalue safeboot  Reboot once more and Windows will  automatically start with AHCI drivers enabled. Then install ubuntu ALONGSIDE Windows for dual boot.
The pc came with windows 10 installed. I created a partition and tried to install Ubuntu 20 mate. I got message about need to disable intel rst. I tried that through bios and got a bsod and a warning about inaccessible boot drive. Any suggestions on how to proceed?  
Dual boot (windows and Ubuntu) on optiplex 5090.