Always include exact PC model in your posts. 

It's safer to install BIOS updates entirely outside of Windows.  So download/save the BIOS .exe file onto an empty (non-bootable) USB stick, not larger than 8 GB. 

Then do a normal, full shutdown, not a Restart from inside Windows.  When PC is off, plug that USB stick in and power on. When you see the Dell splash screen, start tapping F12.  When the menu opens, select the flash update option.

Use tab key to navigate around the update screen. Typically, you don't have to make any changes, aside from selecting the BIOS update .exe file on the USB stick.  Then tab to Start button and press Enter.

PC will restart itself automatically multiple times, and might even look like it's off and not doing anything. Just leave it entirely alone until you're safely back at your desktop.

I had this same thing happen, except I updated to 2.18.1. My pc is xps 8940. I called Dell Support and they tried installed it several ways and then they even tried 2.19.1 which just came out but that didn't work either. Then they downgraded to 2,17. But still that didn't fix the issue either.

After this BIOS update to (2.18.1 originally), I could no longer get into the BIOS with any version installed after that.

When you installed the BIOS, it did some things in windows and then said to reboot, but on reboot it never showed any of the stuff it does when updating the BIOS; like the black screen with the progress bar where it says that it is flashing things, etc.

Instead, it just had a black screen for 30-60 seconds and then it booted back to windows.

Dell is going to replace my mother board.

Oh, and one other thing,...after I updated the BIOS when windows came back up the BIOS was still 2.17 but if you tried to run the 2.17 installer, it would warn you that you were downgraded even though windows said it was at 2.17. But downgrading didn't fix things. You still had no access to the BIOS. F12, F2 and cont+Esc did nothing. All you got was a black screen and then a boot back into windows. But at least I can still use the PC.

Just wanted to add that the Support Tech that I got was really great!

@Kev914z  Where is it still showing BIOS 2.17, is that in Device Manager?  In that case, that probably is the last BIOS version number installed via Windows Update, rather than by you running the .exe file yourself. The BIOS version number doesn't get updated in Device Manager when the update is run manually.

Try this: Click Start>Run>(type in:)msinfo32.exe and press Enter. Click Summary in left pane and scroll down right pane. Tell us what version of BIOS is listed there. 

It is showing BIOS 2.17 in the system information even though the last BIOS version that was installed today by the Dell Technician was 2.18. The problem that it only does part of the update. When the PC restarts it should bring up those screens where it shows the progress bar while it flash stuff and other things. Instead you just get a black screen and then windows starts up.

I think I am opening what you suggest, I just search for system information and click on that. Didn't remember the actual file name.

@Kev914z​ 

Check you Windows Update History. If you don't have Capsule Update unchecked in the BIOS, Windows will try to force it down. You don't see it being installed either.

In any event, I'd call back Dell Support... and tell them that the BIOS version is NOT showing what they installed. See what they say.

Possible you have a motherboard problem and one last thing I'd try, remove the coin cell battery and let it sit out for a minute or so. Possible the battery is even weak, so if you have a new one handy, use it. You might have to check the BIOS setting as well after putting it back... and especially the RAID/UHC one and make sure it is on what you had before (I assume you changed it to UHC).

@Kev914z   - If System Information (msinfo32.exe) says BIOS 2.17, that's the currently installed/running version.  If an update doesn't run completely, BIOS will revert to last successfully installed version. So you're back to 2.17. 

Did you or tech support try installing the latest BIOS update via the F12 flash update method, as I posted above? 

And it's always possible the CMOS chip on motherboard has a problem which prevents it from being flash updated, so that would require a motherboard replacement.

Well, they came yesterday and replaced the motherboard, but it wouldn't boot. Just had a white power light. Put the old motherboard back in. It would just have a black screen for a bit and then windows would appear and I was able to use the PC. Came back today with a new processor and another motherboard. Tried the new processor, but wasn't able to get into the BIOS so he installed the new motherboard. Wouldn't boot up. No errors. Nothing on the screen. He replaced the original motherboard. Had blinking lights which he said were memory related. Tried reseating. Still got the errors. Only put two. Get a white power light and then the DVD drive blinks. If you wait a bit, the DVD drive will blink again. But that's all that it does.  Not boot into windows. Nothing on the screen. If you shut the computer  off by holding the power in, it will start up by itself and just do the blinking DVD bit. So I guess I have to sent it in for service.

The RAM blink code might be referring to RAM on an add-in (AMD or NVidia) video card, assuming you have an add-in video card. 

Physically remove the add-in video card  from the x16 slot and try booting with monitor connected to one of the onboard Intel Graphics ports (HDMI or DP).