Question black screen and crashes on r7 260x

[JustAnotherUser1825]

pc specs:
sapphire r7 260x 2gb OC
core 2 duo e 7500
power supply 500w (don't remember the brand)
4gb of ram (I think its ddr 3 1333hz)
don't remember the mobo (can figure it out later if needed)


so i gave this old pc to a friend (his pc is broken) and now some random crashes happen on all games and the screen goes black when browsing
for a few seconds(it returns to normal NO REBOOT NEEDED)
when emulating games the emulators close after some time.
while playing Dragon Quest 11 and Bloodstained this is the error he gets:
D3D11Util.cpp] [Line: 182] Unreal Engine is exiting due to D3D device being lost. (Error: 0x887A0007 - 'RESET')
after the crash the game closes and he loses all his progress.

this happens very often and its pretty annoying (20 min to 2hrs).

I've tried:
installing a lot of different drivers (always unninstalled the "current" driver with DDU first).
downgrading the core clock from 1100 to 1000 and mem clock from 1625 to 1500. (helped a bit, made the crashes take a little longer to happen)

can someone help me please!

 

[rgd1101]

make and model of the psu?

 

[JustAnotherUser1825]

I don't know the exact brand but I'm 100% sure its not really 500w (it's something between 300 and 400)