Start by explaining or putting up a pic of exactly everything you have connected and power connected to.
Have you connected up all vga connections? pcie power connectors to video card, can you get into bios at all, is dvi or hdmi cable connected to monitor?
Is the ram fully seated? cpu fan header connected to a source?
if the computer turned on, i could diagnose it, the computer does not turn on after me sleeving, the light on the motherboard turns on but does not power if i press the case power on or the motherboard power on
this occurs with all cables connected or with no cables connected