PC freezes with grey screen with vertical lines during Gaming

So over the last few days I have experienced constant crashes & freezing during playing any game or benchmark & the same problem happens for each app..PC freezes with grey screen with vertical lines & buzzed sound, sometimes it's red or yellow but with the same vertical black lines & few times it freezes with black screen but no blue screen error appears..this problem happens after only 2 or 3 minutes of running the game or benchmark & I have to make a hard reset in order to get things back to normal but also artifacts appear at bios start up & some vertical lines at windows logo then a black screen & I can't get to desktop..after unplugging the power cord & vga cable or after few resets pc boots normally without artifacts & I can get to desktop...So I have made many tries in order to get thing back to normal but in vain & I'll state them after the rig specs & status.

The specs are:

CPU: i5 4590
GPU: Sapphire R9 280x Tri-X: 1020 core clock - 1500 memory clock
PSU: EVGA 600W Bronze
Motherboard: Gigabyte B85-HD3
RAM: 2X4 Kingston hyper x fury
HDD: 1 TB WD blue

Temperatures:

CPU: avg 37~40 at idle .... avg 60 at full load

GPU: avg 39~46 at idle .... avg 70~80 at full load

Voltages:

GPU: 0.850 at idle ... 1.256 at full load for core clock & 1.600 for memory clock

So I have made the following failed attempts:

- reinstalled gpu driver many times with different versions.
- reinstalled windows 10 two times with different builds.
- installed windows 7 & then windows 8.1 which is the one am working with now.
- removed cmos battery & updated bios to latest version.
- underclocked gpu to 940 for core clock & 1250 for memory clock without changing the voltage.
- raised fan speed to 70% in full load instead of 53%
- made a memory test with memtest86+ but for one pass only for each stick & there were no errors at all.
- checked hdd with chkdsk & there were no errors.
- made stress test for cpu with occt & prime & there were no errors & temps were normal as I stated 60C
- & this test was an interesting one as I made a stress test for video memory with "video memory stress tool" & there were no errors at all..I was surprised as those artifacts indicates that my gpu is going bad & there is something wrong with vram.
- tried another monitor with hdmi as I use a led monitor with vga cable.

There are important things to mention:

- I have made an overclocking for gpu few months ago..but unfortunately I can't remember the exact values but I thinks they were 1120 for core clock & 1750 for memory clock & it was stable till it crashed 2 times after few weeks of overclocking & I thought that it was strange as if the overclocking wasn't appropriate why I haven't experienced artifacts at the beginning.. anyway I have lowered it to 1100 for core clock & 1650 for memory clock & the system was stable till the strange crash with grey screen happened one time while I was playing COD WWII & I had to make a hard reset for pc but it didn't happen again till I had these recent constant freezings am experiencing now.

- I have tried another gpu of a friend which is GTX 750Ti & games worked normally without any crashes so I believe there is no problem with ram, cpu or motherboard & the problem is with gpu or psu as gtx 750ti needs only one 4pin connector & on the other hand my r9 280x needs two 8 oin connectors so in my opinion it's not a solid experiment that I can determine that the issue is about gpu only

Finally, the problem is that I can't try my gpu in another rig that can handle it as I don't have any friend that has a solid psu..so if there are any other solutions that can fix my problem or at least to determine whether the problem is from gpu or psu or another component, I'll be so grateful & thanks in advance.