Ur kinda over reacting on this, Open her back up look everything over, atx plug, 4pin cpu plug. Just give it good lookin.
Did it used to recognize hdmi monitor? If yes maybe reseat the video card? Still having problems see if you can try maybe dvi monitor instead of hdmi.
Someone help me out here if im wrong but if mouse n keyboard dont light up that means its not getting past bios splash screen.
Look in your motherboard manual and see if there is bios reset jumper or button and then try starting pc again.