My display is going black! Need help

[tuaha khalid]

I have a sff desktop Hp 800G1 
Spec: i5 4570 ,8gb of ram , 1tb hard
I have connected an external gpu XFX RX480 8GB using an external power supply and pcie extention cable 
Now the problem is when i start gaming all things work fine but suddenly after some time 20-30min later display turn black saying no signal going to power saving mode this same happens every time
I dont know whats the problem and which part is causing it

[Kpite]

Its more than likely a GPU connection issue, I would first double check connections and plugs (inside and out). Do the GPU fans still spin when this occurs?

[tuaha khalid]

Yes

I have checked my gpu in my friends pc without pcie extention it worked fine

He gamed for more than 4 hours

[BaconLord222]

13 hours ago, tuaha khalid said:

Yes

I have checked my gpu in my friends pc without pcie extention it worked fine

He gamed for more than 4 hours

have you tried a different cable to connect the GPU to your monitor?

[tuaha khalid]

Yes tried another vga cable

[tuaha khalid]

Now i have also connected my gpu directly to the motherboard to test wether the pcie extension cable is causing the problem but still problem remains