Welcome to the forums, newcomer!
We're going to need a little more information. Please parse the specs to your build like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
If you're recycling any parts from an older build, do mention their age.
If you're connected to the motherboard's display output ports and your processor lacks an iGPU, you won't be getting display out. If the PSU is lackluster in build quality and wattage, then that can be a problem as well. Incompatible hardware can also be another cause.