Messing with Old Hardware that doesn't like me...

[@neongenesis2979]

Some of the older HP OEM motherboards absolutely HATE any "newer" Graphics Card that uses UEFI bios. I would check to see if the onboard VGA is producing a signal.

[@NordicNjal]

You have to use the motherboard vga port i would say.

[@MasonPushman-wd7rp]

I would try the analog on the motherboard, but it looks to me like it could be a board or even cpu issue. I don't have too much experience with old-style computers though.

[@BrunodeSouzaLino]

Even some of the BTX motherboards used regular ATX connectors for power. I have an Optiplex 755 tower which can fit any ATX power supply.

[@Mirra2003-f9s]

Those old HP Pavilion Asus boards were notorious for failing

[@SeeJayPlayGames]

Yeah, ATX hasn't really changed too much over the past... nearly 30 years? (looking it up on Wikipedia...) yeah, it was patented in 1995. I mean, it has and it hasn't. It's only at version 3.0 today, and the 24-pin and 4-pin cables have been around since 2.x. The first PCs I ever built were "AT" standard. ATX wasn't fully adopted by the market for another year or two. At first the main power connection was only 20-pin, but that evolved, and that's why you see older ATX power supplies with a 20+4 pin connector. During the time of the Pentium 4, processors got kind of power hungry, hence the "P4" auxiliary power connector. I don't know they're called that because it's a 4-pin power connector or because the Pentium 4's hunger for power mandated their use, either one is just as likely. I think the former explanation is more likely, since Athlon motherboards also had the same connector.