BenQ GL2480 monitor connected to Mac mini turns black screen on startup

New Monitor = Black Screens on startup of Mac Mini 2018

Hello all, I wonder if you know anything about this type of thing.

tl;dr: I bought a second hand monitor, which works fine but prevents my system from booting up properly.

The new monitor is one of three. If it's plugged in, everything's just black upon powering the Mini. If I unplug the new monitor, all boots up as normal. I can then plug the monitor in and carry on as nomral but it's a big pain getting round the back of my desk each time. Would love to solve this!

I think I have a bit of trouble with the power bus, some times peripherals don't power on and I need to unplug another to make it work. Wondering if it's something to do with that.

THANKS!

Here's my full spec:

# Hardware Overview:

Model Name: Mac mini

Model Identifier: Macmini8,1

Processor Name: 6-Core Intel Core i7

Processor Speed: 3.2 GHz

Number of Processors: 1

Total Number of Cores: 6

L2 Cache (per Core): 256 KB

L3 Cache: 12 MB

Hyper-Threading Technology: Enabled

Memory: 64 GB

System Firmware Version: 2020.0.1.0.0 (iBridge: 21.16.365.0.0,0)

OS Loader Version: 540.120.3\~37

# Graphics/Displays:

Intel UHD Graphics 630:

Chipset Model: Intel UHD Graphics 630

Type: GPU

Bus: Built-In

VRAM (Dynamic, Max): 1536 MB

Vendor: Intel

Device ID: 0x3e9b

Revision ID: 0x0000

Metal Family: Supported, Metal GPUFamily macOS 2

Displays:

BenQ GL2480 - Via VGA/Thunderbolt adaptor:

Resolution: 1920x1080 (1080p FHD - Full High Definition)

UI Looks like: 1920 x 1080 @ 60.00Hz

Framebuffer Depth: 30-Bit Colour (ARGB2101010)

Display Serial Number: J1***019

Mirror: Off

Online: Yes

Rotation: 180

Connection Type: Thunderbolt/DisplayPort

DELL 2407WFP - Via VGA/Thunderbolt adaptor:

Resolution: 1920x1200 (WUXGA - Widescreen Ultra eXtended Graphics Array)

UI Looks like: 1920 x 1200 @ 60.00Hz

Framebuffer Depth: 30-Bit Colour (ARGB2101010)

Display Serial Number: CC***03S

Mirror: Off

Online: Yes

Rotation: Supported

Connection Type: Thunderbolt/DisplayPort

PHL 322E1:

Resolution: 1920x1080 (1080p FHD - Full High Definition)

UI Looks like: 1920 x 1080 @ 60.00Hz

Framebuffer Depth: 30-Bit Colour (ARGB2101010)

Main Display: Yes

Mirror: Off

Online: Yes

Rotation: Supported

Adapter Type: DVI or HDMI

Adapter Firmware Version: 2.19

[Edited by Moderator]