There are many steps to booting. Did you manage to get to the BIOS?
What can you unplug?
I turned off my PC during a Snow Storm because the power was flickering. My PC came out of sleep state and then I turned it OFF, all was good untill the next day when I powered it up, the processor fan, all case fans, power supply and videocard fans were all running, the HHD LED was working, the motherboard LED was On but there was no display on my monitor and no power to the keyboard, mouse and WI-FI USB dongle. even the front USB ports are not working. Is it my motherboard that is fried? I have Windows 10 64 bits and a MSI 970 Gaming motherboard.