Ok guys, here are some news on this topic.
I got the Pentium 4 (Asus P4P800) motherboard to work perfectly well with the nVidia GeForce 7300GT AGP graphics card (I just didn't install the drivers because I was just testing it)... I then restarted the PC to enable the CD-ROM in the BIOS, I then heard some hissing noise and that's it, it started to not powering on again just like it was doing at the beginning... maybe a capacitor died ? Do you think that if I bring it to a computer repair and make them change all the capacitors it might work again ?
The Abit NF7, on the other hand, still turns on, powers on perfectly, very loudly and lightful... but I still get NO VIDEO with whatever card I use, I tried all of the AGP cards (except the S3 Trio, it has the things backwards because it's a 3.3v card, apparently), I also tried with the S3 Virge (PCI card) with every single PCI slot, no video with anything, it doesn't have any built-in VGA, so that's the best I could do...
Now I found an hardisk with a Windows XP installation from 5th January 2005, which probably was originally on either the Pentium 4 or this Abit NF7, it has some nVidia drivers which I ain't sure if are graphics card drivers or chipset (the Abit NF7 has an nVidia chipset !!!)... I'd love to pair that hardisk back with the motherboard I used it 11 years ago !!! It has a lot of stuff and installed games, the drivers already installed... it's basically a "plug and play" hardisk currently... just as long as I get one of those mobos to work.
Currently assembled vintage computers I own: 11
Most important ones:
A "modded" Olivetti M4 434 S (currently broken).
An Epson El Plus 386DX running MS-DOS 6.22 (currently broken).
Celeron Coppermine 1.10GHz on an M754LMRTP motherboard