Either Gpu or integrated graphics work, but not both.

Hi. I had my computer transported to my college city. Before transport worked fine. I returned and after connecting all the wires needed i turned him on. Black screen while i had the VGA cable to the graphics card(but the gpu fan was still spinning). I plugged it in the motherboard and i had graphics again. The problem is that after a restart i had the same black screen while the VGA was plugged in the motherboard and when i plugged it again in graphics card worked.

If one of them wokrs but not both at the same time, could it mean that i have a motherboard problem or a power supply problem (since my gpu draws power only from the motherboard)?

If it helps my gpy is an Nvidia GeForce 640 my motherboard is Asus P8B75-M and my power supply is ALLIED SL-8500BTX (max 500MW)