Question PC fans and lights on the motherboard are working, but my display doesn't receive signal

Jul 23, 2019
My PC isn't working. I started it today and worked fine. I went away from it like 30 minutes, because a neighbor rang at my door. When I came back the screen was black and I thought it went into standby. I moved the mouse around to start it, pressed some keys but the display stayed black. I pressed the restart button and nothing happened. I switched it off from the smps and started it again from the power button. My screen says no input found. I removed the graphics card to check it out for any damage. It looks alright. The screen works. I plugged it to a laptop and it worked fine. I tried plugging the VGA cable directly to the motherboard, but still no signal. I searched on internet to see similar problems and I think that my smps might be the problem. I have lights on the motherboard, the fans are spinning, but my two case lights aren't on. Does this mean that the smps doesn't give enough power to get the CPU running. Do I need to buy a new power source? Is it another problem then?