Re:  If this turns out to be the problem, I will be very annoyed! I will be very annoyed too!  As from my first post 'til my last post, I suggested repeatedly to focus on the video card and assumed that you already tested with a Quadro at some point.
NB: I have seen other threads with similar issues, but no solution for me yet. Dell 5610. Dual E5-2697V2. 128 GB 1866 RAM. SSD running windows 11.  These systems don't have on-board graphics, so I put a little passive GPU in there. Essentially I power on the system and the monitor gets no signal (I don't mean a black screen, I mean no signal - like it goes I to power-saver mode because it's getting no video signals) and then windows boots and there's video.  All drivers etc. Are up-to-date. I have tried multiple monitors and different types of video cables. Over tried removing peripheral. I've done the CMOS battery removal (left it out for an hour and pressed the power button for a while to make sure the capacitors were empty) to reset bios and it does nothing. Trying to boot to recovery from within windows (and the shift + restart trick).Tried just hitting F12 till windows loads. Tried with F12. Tried f2 and 12 alternating.  I've even tried using a serial cable to try and get I to bios from another laptop using putty - but even serial doesn't put out any data! Is this potentially a setting in BiOS? Something blocks access to bios for security - secure-boot or something? Probably blocking serial port too? Thanks for any help!
T5610 - no video until windows boots