No display on the computer screen

Hello, 

I recently got a new power supply and installed it on my PC. My computer would power on for a second and then turn off (fans and light would come on for a second and then turn off).

I installed a new Motherboard and now, all the light and fans are running fine. However, nothing is displaying when plugged in (with new MB).

I also tried different with cable connection, integrated and dedicated graphics. The situation remains the same. I also checked Checked CMOS and RAM. Both the hardware are working fine.

Please help me!