Hello Tuvixcrc, this behavior could be related to the SATA mode chosen when the operating system was installed on your computer.
The SATA mode on BIOS have 3 settings, IDE, AHCI and RAID. If the OS was installed on AHCI mode, and then you changed it to RAID, the OS is not going to find the appropriate path in order to boot up.
In order to find out if that is the issue you would need to access BIOS and change the SATA mode to AHCI or IDE and try to boot to Windows.
If you change the SATA mode to RAID, you would need to change it before the installation of the operating system.
At this point, if you change the setting, you would need to do a clean installation of the OS.