blackscreen after mac bootup /w DisplayPort cable WIERD FIX!! unplug power

[chrisNova777]

so i wanted to write down + share this wierd fix.. yes i know its 2025. yes i know i have older computers.. i was using a monitor that was lower then 1080p for the longest time because my priorities have always been 2d graphic design + audio but i just upgraded and bought a new 4k monitor with my christmas present gift certificate to  best buy.. finally pulled the trigger + bought on that ticked all the boxes.. vesa mountable.. displayPort + HDMI support, analog pass thru of HDMI audio... etc SOOOO i had hooked it up initially over HDMI and realized i was only getting 30hz and thats wher this problem started.. i ordered a displayPort cable for 10$ from amazon prime and figured it would be easy + id be up at 60hz the next day when i got my cable i realized i just got a black screen after the mac system booted. i was pulling out my hair trying to get this fixed i alwasy got a blackscreen and the fix ended up being so simple but strange..

i have to physically disconnect the power cable on the monitor and replug it back in.. (while the computers blackscreened but booted) and then the monitor will magically come on and work!

for whatever reason i still have to do this everytime i change my resolution from 4k to 1440p etc but its working beautifully. on my radeon r7 260 card, i thought i needed to buy a newer graphics card but it seems the r7 260 is capable of driving 4k display at 60hz over displayPort (similar to the GTX 680, age wise, both have displayport, dvi + hdmi1.4 ports) over hdmi it only connects at 30hz speed and the slowness is not desirable running at half refresh rate! im so glad my 4k display is finally able to be enjoyed at a proper frame rate

the monitor im using is the LG UltraFine 27" LG 27US500-W Ultrafine Monitor 27-Inch 4K UHD ...
im not sure if turning it off and on with the front control would have the same affect as unplugging the rear power connector + replugging in.. its a wierd fix and it may only apply to these cards that are not able to do 60hz over hdmi?? not sure but im happy to have my monitor working in macOS! on mojave (32bit compatible) im really happy with it now that its working at 60hz instead of 30hz i was even thinking of returning the monitor or upgrading my video card but im glad i didnt have to spend any more money!

having two monitors hooked up definately helps when your trying to debug the blackscreen problem as most people reach for the reset/reboot when their screen grows black.