Precision M90 with no video output

Greetings,

in 2019 I've bought a 2nd hand M90, with Win7, but I was able to update to Win10 64. Mine came with a quadro nvidia 3500m installed, and also a spare 2500m, a GeForce7900m and the specific docking station from Dell.

Unfortunatelly early this year it stopped any video output, from the screen itself, as well as from the VGA, DVI and S-video, also on the docking station... 

I had the latest BIOS and drivers, and everythigh just ran OK until that day... I was just surfing on the web (so no overheating), and the laptop was conected to the docking station, conected to the power, charging the battery. No external monitor was attached that time.

Suddenly, the screen is filled with vertical lines for a second or two, and then it goes all black. The music continued playing, so the OS was still working. I rebooted the system, but despite the screen remained black, I could tell everything else was working.

OS still loads, the backlight is still OK, but there is no video signal on any port, from the screen itself, as well as from the VGA, DVI and S-video, also on the docking station...
I´ve already tested with the other spare video cards, and also tryed with another SSD with other OS, other RAM boards, other external monitors, and its still the same. I cant see the initial DELL logo, neither the BIOS options, nor any DELL beep code...
Must I reball the motherboard's graphic conectors? Has any of you had this problem also?

From what I've found on ths forum, the problem seems to be always the graphic card, but in this case, are the 3 of them with the same problem?

Kudos