Followed this guide and installed Ubuntu to duel boot with Windows 10, no issues, now have duel boot system   [URL]  
I'm looking for help after spending a couple of afternoons looking and failing to find a solution to my problem. I have an old Latitude E6220 PC that has had a new 125GB solid state hard drive installed and Windows 10 has been installed on the drive. I want to dual boot to Ubuntu which is something I have done many times before on other PCs I have in the house but never on this laptop. No matter what settings I change I cannot get a Ubuntu Live USB to show up as a boot option under the Legacy boot choices. The only choices are HDD and NIC. Info: Bios is A02 There is no Secure Boot options anywhere in the Bios Read about switching from Raid to ACHI but when I do this the USB drive is not found and Windows fails to boot! When I insert a Windows Live USB (Install / Recovery USB) this is seen by PC and it appars as an option in the Legacy boot choices When I insert a CloudReady Live USB this is seen by the PC and it appears as an option in the Legacy boot choices Changing between UEFI and Legacy in Bios does make the Ubuntu USB appear. I am using the same type of USB drives in all 3 examples I have created the Ubuntu USB drive in Windows and Ubuntu with MBR and GPT and FAT32 and NTFS and see no changes As the PC is seeing the other drives it suggests to me that there is some sort of flag or label on the Windows and CloudReady USB drive that is not on the Unbutnu drive but I don't know how to identify what it is. I'd be very grateful of some help as I've made no progress since I started looking into this.
Dell Latitude E6220 Ubuntu Install Problems