I really hope that this does not turn out to be a duplicate question as I'm really confused and tried many options.
I have a DELL XPS 8920 PC which had a windows 10 installed on it. I tried to install an Ubuntu in a dual boot mode (I have done this before on other systems) but encountered this:
And not the normal options for installing Ubuntu alongside, etc. The problem seemed to be with the fact that my system's SATA configuration was set on RAID, people claimed that changing it to ACHI would enable Ubuntu to detect my hard drive with the risk of not being able to boot back to windows. I did the steps recommended in https://samnicholls.net/2016/01/14/how-to-switch-sata-raid-to-ahci-windows-10-xps-13/#fn-513-3 and after a reboot, I wasn't able to boot back into my windows and still ubuntu installation was unable to detect my hard drive.
Note that I am mainly a Linux user and rarely work with windows and am totally unfamiliar with windows low-level configuration. I only want to be able to install Ubuntu, preferably while keeping the already installed windows (if it hasn't gone completely out of repair by what I've done), but losing windows doesn't matter much to me as I don't have any important files there.
EDIT
OK, I tried the first command suggested in Leftover software RAID data to remove any RAID leftovers, doing that resulted in Ubuntu installation to give me the option Erase disk and install Ubuntu which is good, I just want to know isn't there any hope for my windows?
EDIT2
In the end, I erased disk and installed Ubuntu, of course with some difficulty regarding the grub-install which seemed to have been solved after doing what was suggested in this answer