1| You seem to have mentioned the PSU's make and model generically. We'll need to know them in order to gauge the unit's quality and ofc how old it is.
2| How do you have 6GB of ram on your system? Is it mixed and matched?
3| At what resolution are you playing GTA V?
4| With only the iGPU, I doubt you can play any of today's game titles apart from testing by trial and error. In fact even the current gen iGPU's have trouble negotiating games at low settings.