I suggest you unplug the PC from the mains and open it up again. Look for any physical damage - signs of burning etc.
If all looks well, put everything back as it was and check all connections to motherboard, drives and cards.
With the side panel off and making certain nothing is inside the case, power up the PC and see what happens.
If it works, fine. You can post with details of what you are trying to achieve. If not advise what happens.