Question Black screen with RTX 4090 GPU and LG 34BK95U monitor ?

May 12, 2023
Hi All, I just had a new workstation built and I'm getting a big 'ol black screen on startup. I've tried both display port and HDMI. I get a warning that a mismatch of displayport versions will result in a black screen. My LG monitor has Display port 1.1, 1.2, and 1.4 while I believe the 4090 has 1.4a. My understanding is that it it should be ok with the 1.4 setting. fwiw, I am changing the inputs on the monitor.

GPU - RTX 4090
Monitor - LG 34BK95U

side note - my Logitech G mouse also isn't lighting up when i plug it into various usb ports, which is a bad sign.

honestly, I'm not even sure how to troubleshoot this. Any ideas? I'm using the DP cable that came with my monitor, as well as an HDMI one I had laying around.

any help appreciated.

UPDATE: The VGA light is red on my x670E motherboard. I'm not exactly sure how to troubleshoot but at least that points me in a direction.
Last edited:
May 12, 2023
Recheck all your power connectors on the board. Seems system not receiving power. Also make sure gpu is working in another system if you're getting red VGA light on yours.
that's an interesting thought. the gpu is turning on, however... id the gpu is turning on, does that negate the the idea that some power cable could be loose? I'm looking for the simplest solution here. perhaps something came loose in shipping. thanks for the input
Aug 22, 2023
My suggestion would be to check connections on
a. Motherboard - the 24 pin ATX cable
b. Motherboard - the extra 2x4 CPU cable
c. Gpu 3x8 or 1x12 power cable
d. PCI slot - card is well fitted?
e. PCI riser cables if used - most of them are El cheapo quality and won't work - Corsair gen 4 with the purple stripe works for me
f. Clear cmos - before you do that take pictures of each page (saves you time)
g. The earth of the pc and the earth of the monitor 1. Is the earth connected and 2. Are they both connected at the wall outlet? This should be the case

hope this helps!