In that case, start be removing everything not needed so you’re left with mobo, cpu and one stick of memory and troubleshoot from there. If it doesn’t boot, try another stick of RAM (preferably another brand/model if possible). If that doesn’t work remove the mobo and try it outside the case. Still dead you probably either have a dead mobo, cpu and one of them are damaged. Also make sure you have all power cables going to the mobo installed properly.
Are there any diagnostic LEDs on the motherboard to try and figure out what is wrong with it?
The motherboard was incompatible with the CPU or did you previously had a successful boot? I assume the first one is true.
Got it. If you can get your hands on a speaker it might be really helpful to figure it out. And might give you more details to give Gigabyte. Maybe you could get one from a PC that was about to be thrown away.