Check to see if there's a newer BIOS available and update to that.
After successfully upgrade, set it to LOAD Defaults. Apply
Reboot back to the BIOS
Set it according to 7490. It's the same for all the Dell's.
Mainly just set it to
UEFI enabled
Legacy Options ROMs disabled (might be default)
AHCI enabled
Secure Boot disabled
CPU XD enabled
Wake on LAN / WLAN / WWAN /USB Disabled