Possibly the PSU. Have you tried disconnecting everything from the MB except the 2 PSU plugs? Have you tried booting with the original hard drive installed? Of course if you have done all that I mentioned and it won't post then the only component you have not replaced is probably the CPU. Make sure the CPU socket pins are not bent or damaged. Rarely is the CPU the culprit but it does happen. Also check all the cable connections and the MB to make sure none of the USB ports is shorting on the IO shield.

This Dell support page may help as well.

I'm not sure how I missed it but enabling Secure Boot is what was causing the problem. What started all this was resetting the BIOS to do a clean install of Windows 10. I don't remember if I manually enabled Secure Boot or Secure Boot was enabled when I restored the BIOS defaults but either way it didn't like it. I can change anything in the BIOS just not the Secure Boot. Since figuring it out and getting Windows 10 installed I've updated the BIOS from v32 to v34. I haven't tried to enable Secure Boot with the v34 BIOS. If you're thinking I didn't try hard enough to fix it myself before I posted to the Dell Community -- I dacked with that thing for hours before I gave up and posted. Sorry for wasting everyone's time.

Thanks

I have the same problem on BIOS v34. Reset to defaults, restart, it boots. Then the only thing I change is disable legacy ROM option, restart and it is permanently stuck on black screen. Happens consistently, no matter if the hard drive is connected or not and regardless of other options. I am not even able to use secure boot or uefi because the system will not post without legacy rom enabled. Took some time to narrow it down.

Hi,

i have something similar on my T5810.

It has been re-installed recently with win11, and was running fine for 3 weeks.

Suddenly, no display, no Dell logo, nothing.

Power button lit’s up white.

power supply led’s green.

The only respons is to do a cmos clear.

i can enter bios, and see mem, cpu, ssd.

But when i exit and restart, …..nothing.

I replaced cpu, mem, gpu card, …..nothing.

I changed mainboard….. same issue.

When i try diagnostics from bios, it shuts off…

Power supply is a 425W. I measured all 12v lines, -12v, 12v stb.

When i push power supply test button, all fans runs max.

Am i missing something?

You said "CMOS clear," but did you change the 2032 battery for a new one?

Yes, i cleared it via the jumper, and also put a new cr2032 battery.

i even did this on both mainboards.

they act with identical symtoms?

I’m wondering if this could be power supply related, since i measure all 12V outputs.

i also checked the waveforms with an oscilloscope, and they look fine .

Good job troubleshooting with the BIOS reset.

Only  couple more things I can think of.

Try a different HDD/SSD.

Except for power to the MB and power switch, disconnect everything one by one until you get something onscreen (a warning) upon powering on.  This includes the RAM.  Start with the HDD.  You should then be able to determine the culprit.

Simply reseating the RAM might work.

EDIT:  I reread your initial post about how you replaced things.  Only 2 things haven't been replaced:  HDD and just noting the front I/O panel, though I'm quite doubtful that's it.

I finally found the issue.

After troubleshooting with 2 other mainboards, 3 different CPU’s, 2 types of memory and another PSU…..

it was the “Legacy boot Roms” option……

when this option was disabled (to use secure boot) this issue happens.

no dell logo, no windows visible.

however it looks that the system is doing something, because i see the hdd led flashing…..

the only way back is resetting the bios….

so no issues with the hardware, but i don’t get the clue, why this takes away the screen output…..

The final conclusion of this all, is that the graphics card is not compatible with UEFI boot, and that’s causing the “no screen” experience…..