I am unsure which forum this should be posted into. I think the issue is a change I made in the BIOS resulting in no video/no reboot after powering off then on, but it could be a coincidental hardware failure. Please move if this is not best place. (Also thought I had already posted this, but can't find it, so hope it is not a duplicate)
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Well, I managed to pull the pin on a grenade. I was trying to solve a connectivity issue, and was following this wiki

https://en.opensuse.org/SDB:Realtek_8169_driver_problem

and had done #2, then restarted. The power turned on (fans spun), but no video output, no beeps, no lights by eth cable on back of computer.

This confounds me as I would not expect the change I made (enabled wake on LAN in BIOS) to brick the mobo, and hopefully there is some way to restore.

Following this revolting experience, I am reluctant to experiment.

Anyone know how to recover? Thanks.

Dell XPS 8700 Desktop i7-4790 16GB RAM dual boot Win 10 home on HDD / Ubuntu MATE 18.04.1 on SSD

Hi:

I hope you can disable what you enabled:-

Can you get into the BIOS to undue the change you made?

Ztcoracat, thanks for yours. There is no way to get into BIOS without video. When power turned on, fans spin, but absolutely no video output, no beeps, no lights by eth cable on back of computer with or without hitting BIOS boot key (F12). Mobo light on at all times, and when pressed, the case power key lights up, but nothing further except the fans coming on and staying on.

I have no idea whether this is as a result of my BIOS change, or whether it is a purely co-incidental hardware issue. Now trying to trouble shoot the latter, so any ideas welcome.

Dual video cards??
May be wrong selected.
May have to reset bios.

Are you suspicious that your GPU died?
I'm thinking that if you have your Ubuntu install disk try booting that up and set it to nomodset mode, download and install the drivers and etc.

https://askubuntu.com/questions/1620...have-to-fix-it

Does holding down CTRL + ALT + F1 or F2 give you anything?

W/o video I don't know how you could boot a Live Linux CD to get your files. Sorry.

Maybe look for a way to reset your BIOS? This would be the last thing on my list to do until you find another solution.

https://www.dell.com/support/article...system?lang=en

How to fix a black screen in Ubuntu.

https://www.google.com/search?client...31.vxoxBBJPL3I

I'm with jefro....resetting your BIOS is certainly an option.

I agree witb jefro but probably a coincidence. Try clearing the cmos memory by removing the battery.

Thanks for all the great suggestions, however here is an update:

This just keeps careening around. Decided to try a SVGA cable and it works fine. Gets video to monitor, so looks like either the video card DVI circuit, the DVI cable, or the DVI port/circuit in the monitor has gone toes up. Will buy another DVI cable tomorrow and see if that is it. In the meantime, will continue with the SVGA.

That's the good(?) news. The bad is that it has stopped dual booting and will only boot into Windows. So either,

the previously unused, but 2 year old SSD has crashed (it does not show up in Windows file explorer), or

the bootloader isn't facilitating a dual boot.

The former seems the less likely (plus I am unsure how to test a SSD), so I suspect the bootloader?

With this information, any modifications to priorities in the last three posts, or should I try to troubleshoot the bootloader?

You can 're-install Grub' with your Ubuntu CD/DVD.

https://howtoubuntu.org/how-to-repai...ubuntu-live-cd

Here's a link for Hard Drive Diagnosing for Windows 10.
https://www.easeus.com/partition-man...indows-10.html

Boot to live media maybe to see status of drives?

UPDATE: By pressing F12 during the boot process that now results in a Windows boot, a screen comes up:

Boot mode is set to UEFI with Legacy OPROM, secure boot off
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UEFI:

Windows Boot Mgr (if selected, boots into Windows)

Ubuntu (if selected boots into Grub Screen and I select Ubuntu, it boots into UM18.04).

The good news is that (1) the SSD seems to be OK and (2) the grub screen is still there, bad news is that the computer does not boot into the Grub screen.

The other good news is that it narrows down what needs to be fixed, i.e., booting directly into the grub screen. How do I do this?

Once you have Ubuntu up and running open the terminal and run:

That should give you the grub menu so you can choose which os you want to boot.

If I read this correctly you say you select a boot order with F12. That order selects the drive/loader the bios knows about. To change default then change default hard drive order in bios.

Can you now boot into Windows and Linux?