What is the exact model number of your system. Also Dell default in the BIOS is RAID, so more than likely if that is the case you would have to change it to AHCI. But do not do it in the BIOS or you will have to reinstall Windows. This web page at Top-Password describes how to do it.
I recently installed a Samsung SSD drive. Since then as I attempt to start the computer before the Windows 10 launch an annoying popup appears stating RAID volume is not defined. It asks to enter configuration utility to setup the RAID drive. How to get rid of this message.  
Annoying popup to setup RAID volume