I've read all the other motherboard splash screen freezing questions, and I haven't seen one like my situation. So I built my computer a number of weeks ago now, and in the last two weeks, on three occasions I have gone to turn it on and it would freeze on the mobo splash screen. I tried to isolate it by unplugging things at the back of my computer, and it appears two external hard drives are the problem. Whenever I leave my computer off for an extended period of time, like a few hours or more, and I go to turn it on again, if those two external HDDs are plugged in, it just won't turn on. It's a pain always having to take them in and out every time I want to turn my computer on, so if anyone has any solutions that would be really handy. My computer's specs are Gigabyte Z87m-D3H, 8gb ram, amd r7790c 2gb, i7-4770.
In some instances I have reviewed, Leaving the External HHD's plugged in to the USB hubs will drain the CMOS battery or it is possible it is weak. I would provide links to validate the circumstances but currently I'm a bit busy & just reviewed your post. Google this & see what you come up with! Hope it helps! Also without reviewing your Motherboard Specs, do you have the USB Charger option TURNED ON?