Optiplex 990 not powering on

When you say you made another PC out of it, do you mean you did a case swap? Also which form factor of 990 do you have? If a case swap this YouTube video and this one may help. Also this page at Harbin Repairs has the adapters needed to use with a non-Dell case.

@JOcean​ Basically yes, new case and took the hard drive and added an ssd. It was sitting some time without a battery, maybe this has caused the problem. The form factor is like a square, can't really describe it

https://ibb.co/NCkw2vs
https://ibb.co/MStmTL6
https://ibb.co/c6RwVSd
https://ibb.co/KKhFFpX

Maybe those photos will show you what is preventing it from powering on (I also tried shorting the middle pins with the left ones as in the video you sent me, no result)

Just out of curiosity have you taken the I/O board off the original case and plugged it into the MB then tried to boot? If that works then you have a problem with the attachment from the replacement case I/O. Don't assume that it is a specific pin combination on the MB that boots the system. That is why Harbin makes those adapters.

@JOcean​ I have bought this pc not in the original case with gtx 1060. It had the original IO plugged in and it was lying around the power supply so you don't get errors when booting. I have done the same thing again

@JOcean So do you know what can cause this problem? I didn't really understabd about the IO, I disconnected it but it still didn't boot. When I bought this PC it was not in original case, it just had the power button disassembled and soldered together with the case connector. I also tried shorting the pins, nothing worked

I don't know why is everything in blue😂 Sorry for that

I have the cable that I took out, it has 3 wires (Yellow, Red and Black) and a LED. I tried shorting them all together, and yellow with red, yellow with black and black with red but also, no signs of life. I am so confused

@bohdan_08​ So the PSU is the original Dell? Also do not short the wires together as the power switch is a momentary switch not a constant short when pressed. And you do have the original I/O panel connected from the Dell case correct? The fact that the I/O has been modified there is no telling if the wire connections are anywhere close to correct. You would need an OEM I/O to connect in order to start eliminating components as the cause.

It's not an original PSU because there is also a GPU which needs 6pin. I have the IO with USBs connected good and the power switch wire. It's really weird, I basically just put it together like it was (at least I think so), but the power switch connector from the case was cut off, the power button was also cut off the wire, and they were just soldered together. I desoldered them because I used that case for something else. The black and red wire lead to the two left pins on the pwr switch connector, as I read is you short them it boots the system but it didn't. Also there was a yellow wire, I also tried it with red and black, then connected them all together, no result. It is honestly very weird

With a system that has been modified (read sliced and diced) like yours, anything could be the cause. But my money is on an improper I/O connection.

Possibly this YouTube video may help. And did you have a look at the Harbin web page here?

@JOcean​ Which one you mean? The USB one or the power switch one?

@bohdan_08​ Power switch as the USB would not make a difference unless it is shorted and that would be a problem.

I don't think there is actually something wrong with the connection if you mean the power one, because I have tried it with everything: screwdriver, adapter, plugging the power button connector straight into the 1 and 4 pins, no result