Graphics card issues

[Joke366]

Hello everyone!

So, two ago I bought a PC from a retailer here in Croatia. It worked perfectly and I am quite pleased with it.
Anyway, a few months ago I bought a DP cable and connected it all up... My PC instantly crashed and refused to boot up (it was stuck in a bootloop) until I disconnected the cable. Ever since then some random graphical errors occurred every now and then. I played a game that was quite GPU intensive (above 90% GPU usage at any given time) and after a few minutes my secondary (1360 x 768) display turned black with a "no signal" message, while my main (1920 x 1080) display started lagging and it started displaying black frames every few seconds (those black frames were on screen for about a second). It crashed after about a minute of that.

I booted it up again but nothing was being displayed on the screens. I'm using a mini-DP port and a mini-HDMI port on my GPU. When the larger display was connected to the mini-DP port it wouldn't show anything but if connected the other way around (the larger display to the mini-HDMI port) it would display on both the screens. 

After messing with those connections I decided to run FurMark to check if the crashing was GPU-related (it was relatively obvious the GPU was to blame, but I wanted to make sure). The FurMark test crashed after about 2 minutes.
I read up on the internet and concluded that underclocking my GPU was the next logical step. I underclocked both the memory and the core by 100 MHz. Started up FurMark and it ran for 30 minutes without any issues. I thought I had solved the problem... Yesterday the same thing happened - I was playing a GPU intensive game and it started having the display bugs and it ultimately crashed even when it was underclocked. I lowered the GPU clocks by another 50 MHz and it seems relatively stable for now.

I would like to know if you have any ideas as to what the problem might be. Is it even able to be fixed or should I buy a new graphics card?

Thank you for any and all answers!

[RGProductions]

Seen this with dp a fee times but never found out anything else. My guess is bad cable.

[SkilledRebuilds]

Check cables first...

 

Then...if still happens...Return it for testing.

(Record it crashing with your phone and show them that too, if they show that they would be hesitant in a quick recovery)