Refresh rate query with new monitor

[Chopper3]

Hi, I've been running for years with an EVA 980ti connected to a 120Hz Benq XL2420TX via DVI-D. Today I got a new AOC AG241QG monitor (2560x1440, g-sync, can do 165Hz) I've connected to DP port 1 via 'StarTech' 5m DP 1.2 cable but for some reason I cannot select the option to switch to a frame rate than 24hz even though 59, 60 and 85Hz are listed - the display goes black and eventually I switch back to 2560x1440@24Hz - there's not even any higher frame rates listed than that - and yes I've installed the latest monitor driver.

I can't say I'm not a little confused tbh, any ideas? I'm thinking the cable might be the problem but I need a 5m cable.

 

[Chopper3]

Ah there was a 2m DP cable in the box, I moved the monitor over to test it and all modes were listed and I could connect at 165Hz, so it is the cable - bugger, not sure if there are many other DP 1.2 5m cables about