Inspiron 5680 (2020) won't turn on after RAM update - old RAM suddenly doesn't work anymore either

If the MB is totally bricked you would never see an error code depending on how bad the damage was with the RAM placement and the RAM falling out as you described. Have you tried leaving the CMOS battery out for 15 minutes before reinserting? Also try replacing the CMOS battery with a new recently purchase battery.

If you have an add-in video card (AMD or NVidia), are you sure you're connecting the monitor to that card, not to the onboard DP port?  An add-in video card would be in the area marked "6" and "7" on back of PC.

When you have only 1 RAM module, it should go in 2nd slot from CPU. When you have a pair, they should go in 2nd and 4th slots from CPU...

@JOcean​ Thanks! This gives me hope! I have taken out the CMOS, but only for a few minutes - and I have replaced it. I tried to deplete the remaining electricity by keeping the on-button pressed for 20 seconds. I also tried to reset the CMOS by moving the jumper pins in the way suggested by the manual:

https://www.dell.com/support/manuals/en-us/inspiron-5680-gaming-desktop/inspiron5680_servicemanual/procedure?guid=guid-9121b45b-cf05-4d91-baf0-62f61bf65434&lang=en-us That too didn't work.

@RoHe​ Hi, thank you! Your comments in the other thread linked above have already been very helpful.

I still have the original video card that came with the computer - GTX something. There is only one hdmi port that I have always used and continue to use, so that shouldn't be the problem.

I have tried multiple positions, including the two you mentioned. The original 8GB ram stick was inserted in #2, counting from the CPU. However, neither the original stick works in that position nor the newly acquired two 16GB sticks in #2 and #4.

Run the PSU BIST, following instructions for a PC with a built-in PSU diagnostics button. 

What color is PC power button and steady or blinking when there's no boot? If it's blinking, count the blinks which is an error code.

Have you double-checked all the cabling to/from the motherboard and to/from front panel? Could you have accidentally dislodged a cable connector, or PCI-e card, etc?  Sometimes things look okay when case is open, but get dislodged when closing the case.

If your GPU needs an extra  PCI-e power connection directly from the PSU, make sure that cable is correctly connected to the card.

If your monitor has a DP port, you could remove the GPU and connect monitor to the onboard Intel DP to see if the GPU failed.  You have to physically remove the GPU, otherwise the onboard DP port may be disabled.  Or, if you have another HDMI monitor and its own HDMI cable, try them one with this PC.

@RoHe​ Thanks! I verified that the power supply works with the BIST test and I also checked that all the cables are plugged in properly.The LED is yellow and blinks either two or four times, depending on which ports I put the RAM in. So either it's "RAM failure" or "no RAM detected."

My monitor doesn't have a DP port. I think I may need a new motherboard or a new PC entirely. Oh well.

Which RAM did you use in these latest tests, old or new?  I'd only work with your original RAM until you get this sorted because you (we) don't know if the Gskill RAM is actually compatible with this PC model.

Try one old RAM module in 2nd slot from CPU. If no go, try in 1st slot from CPU, then try 3rd and then 4th slot.

Then use the other module from the old pair and test it by itself as above.

BTW: Did you actually install a fresh motherboard battery as @JOcean said?

@RoHe​ Hi, I did use the old RAM in the 2nd slot (and in others, to make sure). I also tried the new RAM. The battery is new.

I have given the PC to a repair shop which confirmed the defect of the motherboard.

Thank you for your valuable info and for your time! This is much appreciated!

Best wishes.

@Tim3000  - You're welcome. At least we tried to solve the problem, but sorry it seems to be the motherboard.

Hope the shop can replace the board quickly and get it back into working condition.