It could be the motherboard is dead. But the mobo won't start if it's not getting any power. Does the mobo have an LED that lights up when power is applied, even if the PC is turned off?
Is the PSU working? Unplug it from the PC and look at the 24-pin plug, use a bit of wire (like a paperclip) to connect the green wire to any of the black wires. If the PSU fires up, that's good news for the PSU, bad news for the mobo 🙁
Remember to also check the simple little things - is the PSU is plugged into the wall properly? Try a different socket. Try a different power lead from the socket to the PSU.