I sold my 750 Ti to one guy, it was working perfectly fine before I gave it to him. Now the guy says his screen is artifacting, after playing games for about 2 hours. (horizontal lines on screen and such) So, is there any way to fix this? What could be the problem? He has a 400W power supply and he doesn't know his other computer parts, could the power supply be the problem? The monitor is working fine btw.