The default setting for SATA Operation in BIOS setup is AHCI, but Dell might have installed Windows on this PC with BIOS set to RAID.  So when you reset BIOS, SATA Operation would be set to AHCI.  If Windows was installed in RAID mode, that could explain the "no boot drive" error message. Remove the add-in video card completely and connect monitor to either the onboard Intel Graphics HDMI or DP port. Then power on and open BIOS setup. Find the SATA Operation setting. Change it to RAID, save the change and exit setup. See if it boots now. If PC boots, reinstall the add-in video card and move the monitor connection back to the add-in card. If PC won't boot or there's no video output now, the video card failed...
We just had a power outage and now our XPS 8910 gives 6 beeps on startup and says no hard drive detected. I checked in BIOS and no HD detected. I replaced the CMOS battery for the heck of it and ...no. I did reseat the video card because it was not seated well (and 6 beeps). It still gives same 6 beeps and no HD detected. Does anyone have any ideas? All help appreciated. Thank you.  Also- I did disconnect and reconnect the data and power to the HD and reboot. I also reset BIOS to default.   
XPS 8910, 6 beeps on startup, no HDD detected