Question Computer won't start without a GPU installed.

[mac_angel]

I have an older system I was going to set up as a Pi-Hole. It's an ITX case/system, and a 4th gen CPU, K version, not overclocked. I can't get it to do anything without a GPU plugged in. I can't remember how, but I had the problem before, a few months ago, and I had a GPU I could plug into it, go to the BIOS, and tell it to boot from the iGPU. It wouldn't work for a LONG time, and then I finally got it to work. I put it away for a while, and got it out today to try and set up the Pi-Hole, but now I'm back to the same problem.
When it starts, no BIOS post, just a black screen and a _ in the top left. I don't have a spare GPU to plug into it any more. Resetting the BIOS didn't work before, or now (shorting the jumper).

 

[SkyNetRising]

When it starts, no BIOS post, just a black screen and a _ in the top left. I don't have a spare GPU to plug into it any more. Resetting the BIOS didn't work before, or now (shorting the jumper).

If you see blinking underscore, this means video signal gets delivered.
It has nothing to do with iGPU working/not working.

This simply means, OS is booting in wrong mode.
If OS has been installed in legacy mode, then you can boot in legacy mode only.
If OS has been installed in UEFI mode, then you can boot in UEFI mode only.

Fix your boot settings in BIOS.
May also want to disable secure boot and fast boot.

 

[mac_angel]

If you see blinking underscore, this means video signal gets delivered.
It has nothing to do with iGPU working/not working.

This simply means, OS is booting in wrong mode.
If OS has been installed in legacy mode, then you can boot in legacy mode only.
If OS has been installed in UEFI mode, then you can boot in UEFI mode only.

Fix your boot settings in BIOS.
May also want to disable secure boot and fast boot.

I can't do any of that without being able to see the BIOS. I know it's getting a signal, but I can't get to the BIOS, Windows, or anything. I don't have a spare GPU to plug into it.
Personally, I think that's really messed up that if it only has one GPU and one display with no other options, it should display on the only thing that's available.

 

[SkyNetRising]

What model motherboard?
What model cpu?

Can you show a photo of rear I/O panel of your pc? (to see, how you have connected everything)
(upload to imgur.com and post link)

 

[Zerk2012]

If it's working you should be able to boot into BIOS since that comes before it tries to load windows.

 

[mac_angel]

If it's working you should be able to boot into BIOS since that comes before it tries to load windows.

I agree. But instead, when I turn it on, I get a black screen with a _ in the top left.

 

[Hellfire13]

I can't do any of that without being able to see the BIOS. I know it's getting a signal, but I can't get to the BIOS, Windows, or anything. I don't have a spare GPU to plug into it.
Personally, I think that's really messed up that if it only has one GPU and one display with no other options, it should display on the only thing that's available.

This has probably nothing to do with GPU, as mentioned above. If you are getting a screen, the iGPU is working.
What do you press to usually enter BIOS? What happens when you try it now?
Seems more like a board issue than GPU. Also, likely that the storage is not detected.

 

[mac_angel]

What model motherboard?
What model cpu?

Can you show a photo of rear I/O panel of your pc? (to see, how you have connected everything)
(upload to imgur.com and post link)

EDIT:

I can't remember. It's a prebuilt micro system that I got from someone that doesn't know about computers. I built him a new one, he gave me his old one. It had a GPU, but I told them to keep it for another system since I didn't need one.
I found my search history. It's a Gigabyte GA-Z87N-WIFI. Latest BIOS, which is from 2014, so not a lot of info there.
The CPU is a 4th gen Core i7, I believe. I know it's a K model, but he never overclocked it. It has an Intel CPU cooler on it.
I know it has an iGPU, because I did have it working before, and it wouldn't be giving me a black screen with a _ in the top left. I also remember I had a bitch of a time with this exact same thing last time. I would tell the BIOS to boot from iGPU first, with a GPU installed, and it would work fine, display from the iGPU. But every time I unplugged the GPU (which I needed in my server, which doesn't have an iGPU), I'd get this exact same problem.

I tried reaching my phone in to snap a pic of the motherboard, looking for model number printing, but no luck so far. I really don't want to take it all apart just to get at it, especially if there's no printing to be found.

and it's hooked up by HDMI. Only thing plugged in is HDMI, a USB for keyboard/touchpad, and a single SATA drive.

 

[mac_angel]

This has probably nothing to do with GPU, as mentioned above. If you are getting a screen, the iGPU is working.
What do you press to usually enter BIOS? What happens when you try it now?
Seems more like a board issue than GPU. Also, likely that the storage is not detected.

as I mentioned, I can't get at the BIOS. Nothing happens when I turn it on, other than black screen and _ in the top left. I can't get the BIOS, I can't get a boot menu, nothing. And the SSD is new, and working. As I also mentioned, this was working a few months ago, but I also had the same problem a few months ago and had to keep fighting with it. I could set the BIOS up to use the iGPU first, but only when I had a GPU plugged in. As soon as I took the GPU out, it wouldn't use the iGPU first any more.
Also, if no storage was detected, it would give that error and let me get into the BIOS.

 

[Hellfire13]

as I mentioned, I can't get at the BIOS. Nothing happens when I turn it on, other than black screen and _ in the top left. I can't get the BIOS, I can't get a boot menu, nothing. And the SSD is new, and working. As I also mentioned, this was working a few months ago, but I also had the same problem a few months ago and had to keep fighting with it. I could set the BIOS up to use the iGPU first, but only when I had a GPU plugged in. As soon as I took the GPU out, it wouldn't use the iGPU first any more.
Also, if no storage was detected, it would give that error and let me get into the BIOS.

The SSD might be working, but it might not be detected to load the booting files.

 

[SkyNetRising]

and it's hooked up by HDMI. Only thing plugged in is HDMI, a USB for keyboard/touchpad, and a single SATA drive.

Your motherboard has two HDMI outputs and DVI output.
Connect your monitor to another video output instead.