Getting Windows to boot again after switching from RAID to ACHI.

http://triplescomputers.com/blog/uncategorized/solution-switch-windows-10-from-raidide-to-ahci-operation/

Dell instructions basically work.

https://www.dell.com/support/article/us/en/04/sln301754/how-to-install-ubuntu-and-windows-8-or-10-as-a-dual-boot-on-your-dell-pc?lang=en