This forum post, an oldie, may help as the user had a very similar problem.

I've just had exactly the same problem. No thanks to Dell, after some hours, I managed to "unbrick" my T3610. Very disappointed with Dell's own involvement on this forum (the little there is seems to be vague, not provide answers or erroneous).

First off (as I discovered) removing CMOS battery or using mobo jumber to "factory reset" BIOS doesn't help; and only results in more work more work as you'll later have to re-flash BIOS with the latest security patched version.

Like you I assumed the T3610 wasn't booting; but although you have a black screen the machine is POSTing and booting. The problem is you have a "pre UEFI" graphics card and UEFI won't communicate with it. I temporarily replaced the old graphics card with a borrowed modern "UEFI" graphics card. Switched the workstation back on and (thank goodness) the DELL logo displayed and I was able to enter BIOS settings. I unset secure boot and "enabled legacy ROMs". Reinserted my original graphics card and all was good. Win 10 errored on booting (maybe fixable) but as I'd only just got the T3610 I had no data to lose so just reinstalled windows.

Another word of warning: Don't assume Dell's Support Assist will correctly identify driver updates - it failed to identify my reset BIOS needed updating - I assume it must have recorded my earlier  (before problem) BIOS update and was designed to assume it was still applied so didn't re-check (sloppy).

Hope this helps someone in same position..

Will definitely try on my Dell T5610 machine.

Which UEFI Graphics card did you use??

@KumarX  Sorry, I've no idea, I don't game, and my previous machine was built in 2007 so my knowledge of graphics cards (and "modern" stuff like UEFI) is minimal. I borrowed two oldish UEFI cards via a friend of a friend and luckily the first one I tried displayed.

If you have the same issue I assume any UEFI card will do the trick.

Things to try and pitfalls.

If your UEFI card/monitor connection still does not display during POST then try one of the other outputs (VGA, DVI, HDMI, DP) from the card  - I've a vague recollection I had to do this.

Once you've disabled Secure Boot and enabled legacy ROMs your original "legacy" card should work with your Dell whether set to legacy or to UEFI (this is certainly true for the old GT545 card in my T3610).

Some UEFI cards won't work with legacy BIOS - so if you intend to switch your Dell back to "legacy BIOS" you might again have a black screen until you replace UEFI card with your original legacy graphics card.

If you were previously using "legacy" but are switching to UEFI (without secure boot) then you will also need to convert your Win 10  drive from MBR to GPT.

I gave the person who loaned the graphics cards a few old components as thanks - but he's not responding  to texts so I'm unlikely to be able to find which UEFI card I used for the fix.

Just a quick update. Some months ago I swapped out my old legacy graphics card for a new low profile Nvidia GT1030. In my T3610 BIOS I've left "secure boot" switched off and my new card works fine whether I've set legacy or UEFI mode in T3610 BIOS.

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I too have had this issue with several of the older Dell Precisions 5610 and 3610's and I'm sure there are some others that fall in this realm.  As others have done I tried to reset the bios by removing the battery and bridging the reset and doing the factory reset.  Sometimes I was successful other times not so much.  I scrapped some of the boxes convinced that they were bricked and they probably weren't.  After reading this I came to the conclusion I just wasn't seeing the bios, but it was there.  I finally found a card that worked it was a Nvidia GTX 750 there may be others but this one does.  I was able to get into the bios and do anything I wanted.  I installed windows 11 on a 5610 and found that it would only show the bios with that card.  Then I tried several other cards in the secondary graphics port and downloaded the windows 11 driver for the GTX 750 and found it would work with the Nvidia Quadro 1800 and the Quadro FX580 and that you could boot to the OS fine with either card.  However you can't get into the bios with either card even by setting it up for recovery and UEFI bios.  But you can run the machine and it will happily boot with secure boot and UEFI just no bios screen without the GTX 750. The bios is probably there you just can't see it or get into it without the right card and this has happened in the legacy mbr mode as well in the past.  I'm keeping this GTX 750 just to mess with any of those machines that refuse to give me a bios screen in the future.

AustinTech

I did it in like 3 minutes, UEFI and SecureBoot enabled in Windows 11 works like charm without data loss.