I recently installed a new CPU cooler in my dad's desktop, since the old one made too much noise. For my own convenience, I unplugged everything, unscrewed the motherboard (Gigabyte GA-965p-ds3 version 1) and put it on the table to work on it. Now that I've put everything back in, I am encountering a few oddities and problems.
First, my display doesn't work, even though my videocard is plugged in and connected properly. The computer starts, the ventilators work (as does the newly installed cpu cooler), but I get no POST beeps. So no display & no POST beeps.
I think the problem is because I haven't plugged anything in the ATX 12v 4pin slot. I have a 24 pin connector, consisting of a separate 20pin and a 4pin, that I can plug in the main connector. If I plug the 24pin in, everything works fine (without the display). If I take the 4pin out and just use the 20pin, everything works fine as well (which is slightly weird to me). Now, whenever I try to put the 4pin in the ATX 12v 4pin slot, it crashes. I have no other 4pin connector to put it the slot, but I do have another 6pin connector (PCI-E), which crashes the pc when I put it in the 4pin as well (although it fits in).
I believe that's probably why I don't get POST beeps and why the display doesn't work, but I don't really know how to fix it. Could anyone help me out?
On most motherboards, the ATX12V 4-pin connection is a requirement for booting so I am a "little" surprised your board boots without it but fails with it.
There is nothing 'odd' about the motherboard working with only the 20pin part of the 24pin main connector. The main reason for the extra four pins is to provide extra 3.3/5/12V power to the motherboard prior to the ATX12V spec where linear regulators were frequently running off lower voltage rails. Today, almost everything uses point-of-load switching regulators running off 12V rails so 3.3/5V power have become nearly useless. With dedicated ATX12V connectors for the CPU and PCIe power for (GP)GPU, the extra 12V pin on the 24-pin connector has also become unnecessary.
While the PCIe power connector might 'fit' in the ATX12V connector, the 12V and GND pins are reversed. Plugging the wrong connector in can fry your motherboard and/or PSU and/or GPU if the motherboard/GPU does not have sufficiently powerful clamping diodes to force the PSU to either shutdown or self-destruct.
@samuelspark: Yes, hehe, I did. It fit in perfectly so I gave it a try. It crashed, but apart from that nothing serious happened. I won't try it again.
@InvalidError: Yes, I found it surprising that it working without the ATX12V 4-pin as well, although I don't hear a POST beep, so it probably doesn't boot but just gives enough power to let the fans run.
With the information you gave me, InvalidError, I quickly found out what plug I needed to use: ther was an 8 pin connector left that I hadn't tried simply because it was 8pin. I plugged it in the 4 pin and everything works flawless now. Thanks!
Yes, I found it surprising that it working without the ATX12V 4-pin as well, although I don't hear a POST beep, so it probably doesn't boot but just gives enough power to let the fans run.
Motherboard-powered fans are powered by the regular 12V supply from the 20/24-pin connector, other case fans connected to Molex connectors are powered directly by the PSU so the absence/presence of ATX12V is irrelevant there. If your computer has a PC speaker and beeps on normal boot but does not beep with the ATX12V disconnected then your PC is not POSTing anymore.
On most ATX boards, the ATX12V is the only power source for the CPU. No ATX12V = disabled CPU = no POST/beep/boot.