Graphics card and slot are bringing issues on my PC

Hi,
I have a newly purchased computer and graphics card. My computer does not work well and I cannot even use it. The person I bought it from was not able to tell me why the card does not work and was really incapable of solving the PC problem. I was told that the graphics card, graphics card slot and the PSU are the cause of this problem. How is that so? Could someone advice please. Thanks.
