Have you checked the BIOS boot menu to make sure that the Windows Boot Manager is first in the list? 
As title says, i installed Windows 10 with a CD, after installing, my laptop boots from the CD automatically instead of the SSD. When i disconnect the CD, then it says there's not a bootable unit.Tried reinstalling but with a USB bootable, when it fininished, the same issue happens, laptop boots from the USB automatically, when disconnected, says there's not a bootable unit. (Which obviously exists because it lets me install Windows) I have a Dell Inspiron 3421, i upgraded the BIOS like 7 months ago. I have this laptop since 2014-2015 i think.
Issue with SSD. After installing Windows 10, BIOS does not recognize the SSD