My New PC Won’t Boot, Any Ideas?

I just built my first PC and am having some trouble getting it to boot. When I power it on, the fans spin, and the GPU fans are working, but my RGB lights aren't turning on. Additionally, my keyboard and mouse don't light up or respond, and the monitor isn't displaying anything, even though it's plugged into the GPU. I've double-checked all the connections and even did a CMOS reset by removing the battery for 5 minutes. I'm also not seeing any indicator lights on the motherboard to help troubleshoot. I've tried switching the RAM around as well, but I'm feeling pretty lost here. Can anyone help?