Ensure the24-pin ATX and8/4-pin CPU power connectors are firmly plugged into the motherboard. If your CPU has onboard video, remove the discrete GPU and display from the motherboard's video outputs to rule out GPU issues.
New Gigabyte B550M Gaming X WIFI6 AMD AM4 MicroATX DDR4 Desktop Motherboard
Gigabyte B650 GAMING X AX V2 ATX AM5 DDR5 Desktop Motherboard
GIGABYTE Z590 Gaming X Motherboard Intel 11th Gen Z590 DDR4 LGA 1200
MSI MPG Z390 GAMING PRO CARBON LGA 1151 Intel Z390 ATX Intel Motherboard
GIGABYTE Z390 UD Intel 8th/9th Gen DDR4 LGA 1151 SATA 6Gb/s ATX Motherboard
MSI MPG Z390 GAMING PRO CARBON LGA 1151 DDR4 HDMI/ DP ATX Motherboard