And......
What is the problem? It looks fine to me (but I am on my tablet, not computer, so may missnclarity)?
Is it the text getting jaggy/unreadable? If so, I have that happen sometimes, and I have no idea why.
Also, I get some games where the meshes and stuff doesnt load correctly.
In both cases usually a reboo, or rather a shut down, then turn back on, fixes the issues. Sometimes 2 restarts are needed.
 
If that isnt the issue, can you tell us what the issue is now? I thought it was fixed with the new cable?
 
Some other things that come to mind. In order to have 4k @60hz, you HAVE to have ALL hardwarthat supports it.
That means the tv has to havethe hardware support built into it.
The cable has to support it.
The video card has to support it.
You cant just use any video card with a (is it hdmi or dp 1.4b?) cable, and plug it in to hardware that doesnt support it.
No software will make it work. No update will make it work.
You HAVE to have ALL devices support it via hardware, ie built into all 3.
If you are sure ALL 3 things support 60hz 4k, try checking the tv settings (osd) for a toggle that you may have to change to get it to work.
 
Do not try to get an hdmi or dp cable (is only dp support 60hz 4k? I remember reading it does, but not sure if they updated hdmi to support it) that is longer than the spec. This will usually lead to problems. Even usb 2.0 and 3.0 have issues with cables longer than the spec, 3 feet, unless they were powered. You cant 'add' extra power to dp 4k 60hz though like you could usb (usb got around this by using powered hubs and thicker interior wiring).
Do you have anything that is NOT specced for 4k 60hz, like the modem, roku (some roku's like the ultra, +, etc actually have built in hardware support for 4k 60hz (wired or wifi. But I thought the spec said it had to be wired, but may be just misremembering).
And, lastly, dvi will not support it. It is not specced to do 4k 60hz.
 
What I am getting at is this is new tech, requires ALL devices involved, or even extraneous devices hooked up to the tv that arent 4k 60hz specced, will cause it to not work.
Make sure you have everything connected that is 100% verified hardware supported for 4k 60hz, and remove anything that is not hardware specced for it (if it says 4k 60hz READY, it isnt. It either is or isnt. It either has the hardware built in or it doesnt). Unplug anything that isnt specced, and try it again, with the tv's osd switch turned on for 4k 60hz.
 
Other than that, I hope you get it working.
Sorry if I said anything not related to your issue, it is late here, and I have not been sleeping well the last week.

I guess you never said what monitor your using  ?  like benQ   seems to know they had a issue with some models of theres   and has rma'ed for folks  [ I think I linked that above ?? ] 
 
anyway what brand and model is it ?
 
this thing been going on for some time   and a lot of ideas  on fixes   this worked that worked had to rma , ect.....
 
http://www.tomshardware.com/forum/id-2952395/displayport-signal-issue.html
 
http://support.benq.us/customer/portal/questions/13047250-benq-display-port-issues
 
with the hdmi best to use the latest  if you  had to go buy  check out the revisions on what each will cover or been improved on 
 
https://en.wikipedia.org/wiki/HDMI
 
I got to tend to agree that it seems when 144 came out a lot of issue came with it . you see all over in forums  on them  [opinion]    with this port thing reguardless   starting with the 900 series its another  you see boocoos  of threads on  .   just one of them things you luck out on I guess .  never tried mine but it may be fubar as well as the rest out there [???]
 
unless you got another as good 144hz monitor to test withj maybe your buddy got one  to help in a process of elimination .     just seems funny the 2 cards a 900 and a 10 series still does it  .  would be bad luck to get 2 cards with the same issue   so I would feel safe its not the cards for now  .  all the cables you tried  ??   how many bad cables can a guy get in a row ?   then you say it went to working fine then out of the blue it started back even with the new 10 series card ?   with that it could be easy to point to the monitor   .
 
sad thing is with this stuff you can find yourself easily chasing your tail  and then add in the money in new stuff to try  .  I get some of that here  don't think your alone

maybe best   just looking  a tad  like in the reviews at  amazon   start with the one ,2 ,3 star  maybe one of them things   with it ?
https://www.amazon.com/Acer-ED242QR-Abidpx-FREESYNC-Technology/product-reviews/B07598HLB5/ref=cm_cr_arp_d_hist_2?ie=UTF8&filterByStar=two_star&reviewerType=all_reviews&pageNumber=1#reviews-filter-bar
 
lot of issues it seems  don't look good on that monitors behalf  ?
 
not much on acer site on it yet ?
 
https://community.acer.com/en/discussion/543504/acer-ed242qr-dvi-not-working-with-asus-rog-radeon-rx-vega-64-strix
 
I liked this answer ..  just puts him in your boat
https://community.acer.com/en/discussion/538267/ed242qr-abidpx-only-goes-up-to-120hz-instead-of-144hz-as-advertised
 
 
another thing I seen was acer owners with like issues  with different models   wondering why there is no win -10 drivers  if this could be another win-10  its the greatest  thing ..lol...
 
may try another OS    you could burn a live dvd of Linux  and see  if things go working under it  . cant hurt and all you need is a live dvd  [ I keep one handy ]
 
 
I seen this pop up a few times like at newegg reviews
 
''Cons:                When you use HDMI you don't get up to 144Hz. But then you get 120 which isn't that bad for grateful people like me. AND IM 11!
 
if you got the revision hdmi cable it should support it easy 
 
sad thing with new egg  they remove bad reviews   not all but just enugh to keep things not looking so bad   [i' had a few removed or lets say ''disappeared'' if something I gave 3 egg or less over time ]
 
just don't know what to say or what to do next
 
burn a live dvd of Linux and pop it in and try it and see ?
 
You can download the Linux Mint operating system for free. It comes as an ISO file
which you need to burn to a blank DVD. The liveDVD is then bootable and provides a
fully-functional operating system which you can try without affecting your PC. In
layman's terms, when you put Linux Mint on a DVD and place it into your computer, you
can try it out while leaving your current system intact.
Note: It is also possible to write the ISO image to a USB stick or other memory device and boot from that,
or to boot from the ISO image on the hard drive, but these options are somewhat more advanced and the
method presented here is recommended. For help with alternative methods of installing and running Linux
Mint, please visit the forums.
 
https://www.linuxmint.com/documentation/user-guide/Cinnamon/english_18.0.pdf
 
it nice to have a quick backup / test OS   that runs / boots standalone off a DVD or pen drive  .    thing is if it all works under it  may point to a 10 issue 
 
even Linux has issue with display port   [maybe the latest has it covered by now  ]
 
http://forums.whirlpool.net.au/archive/2607130
 
https://www.linux.com/news/event/open-source-summit-na/2017/3/fixing-linux-graphics-kernel-true-displayport-compliance-or-how-upstream-patch
 
see in the end I just stick with the tried and true  1080 @ 60  and my good old solid CRT monitors  and avoid this stuff as long as possible .   that CRT nothing come close to replacing it  in gaming cause when your lagging you aint fragging .  and the rest are HDTV's   , but that's just me ..   then like I said I never had to use my display port it may not work right as well for all I know 

 
I guess that's why there are so many posts on so many forums on this all you got to do is google   gtx 9??  display port  or 144hz or ?? issue  .
 
see like you win-10 +NVidia  +144hz  may = issue    not to say 8 or 7 getting the same 
https://forums.geforce.com/default/topic/1015540/don-t-buy-a-144hz-monitor-if-you-run-windows-10-nvidia/
 
https://linustechtips.com/main/topic/754621-benq-xl2720z-at-144hz-working-but-not-really/
 
like here even with the 10 series still with something
 
https://techreport.com/news/30304/nvidia-pascal-cards-still-exhibit-high-refresh-rate-power-bug
 
NVidia has struggled since 10's release    I guess having to work with a service instead of a OS aint helping   and I figure why everyone is dropping support of a lot that under 10  cause they cant keep up   and why here pretty quick   if your not running 10 nothing is going to fully work or if it will work at all .
 
for me I would have to really hate your guts to recommend 10 to ya  to start with  .   and why it referred to as that malware service called windows 10  ,and its not going to get better .
 
seems to me if it is in fact working on your hdmi  best leave that sleeping dog alone  before you loose it as well  .   this computer building has become a joke anymore  a hyped up gimmick filled money grab and everything is buyer beware
 
hope you the best of luck on this .