Question PC restarts when trying to play games !!!

[Leader6234]

HEY GUYS ...👌
I used to play games on my PC with these spesc
PSU : 535 Watts
MB: Gigabyte GA-880G Usb3
CPU: Amd Athlon2 X4 b97 @3200 Mhz
GPU: Amd Hd 5770 1gb D5
Ram: 2x Elixir 2gb dual channel + 4gb Apacer DDR3 ( 8gb totall @ 1600 Mhz)

Recently I bought an AMD Rx 470 4gb (xfx black edition) but unfortunately I couldn't play games because my PC restarts as I try to play, I'm having occasional desktop flickers and visual glitches , sometimes even when playing videos
I can play some games like PES or some lighter games but when I try to play some modern games I can go through some menus n then restart happens...
I tried this troubleshooting method to find out the cause
* Tried different versions and also older graphics drivers from crimson to Adrenaline
*Tried different Ram slots and even a single module in different slots
*Used an assistive PsU to power The GpU Specially in case if there's anything wrong with my main PsU
*Ran windows memory diagnosis n it found no problems
*Checked Temperatures and CPU has 55 °c under full stress(using CPUZ stress tool) GPU has 65 to 75 °C under full load using FurMark GPU Burner n the test goes just fine after several minutes

The point is that my PC doesn't restart when stressing CPU or GPU for a long time but everything becomes unstable when playing games ☹️

So I just wonder what the hell would be the reason my PC acting nuts!!!
What do u think ??
What else should I test ?
Thanks in advance !!!

 

[rgd1101]

make and model of the psu?

test with a different one?

 

[Leader6234]

This is my PsU which is almost 10 yrs old but it used to power my former graphics card just fine

 

[GarrettL]

10 years old, you need a new one.