Are you able to get into the bios or see the bios splash screen at startup, with the monitor plugged into the graphics card? If not, the issue is with graphics card hardware. If you can get into your bios and see the bios splash screen a startup, then the issue is likely software and you need to troubleshoot your drivers.
You could try:
1. Re-seating the graphics card.
2. Installing the graphics card into another pc to test.
If the graphics card doesn't work in another pc, then your graphics card is defective.
If the graphics card works in another pc, then you could try swapping out the power supply.
If the grapihics card works in the seond pci-e slot, then your motherboard is most likely the cause.