newly built

Hello! I've built a new pc, keeping only two hard drives and the gpu. I bought: Corsair Vengeance RGB PRO 16GB (2x8GB) / 3200MHz / DDR4 / CL16 Corsair H100i RGB Platinum Samsung 970 EVO Plus series SSD 1TB M.2 Corsair RM750X V2 / 750W / 80+ Gold Corsair LL120 RGB / PWM / 120MM x4 Intel...

I am building a pc. I got a gtx 750 Ti. It's not displaying. When I take it out and use onboard graphics the monitor displays. But when I plug graphics card in, it won't display. The fans spin. I have tried using vga and HDMI ports.