Your computer power supply has shut down with circuit protection. Look for equipment or leads that have shorted out.
Remove all the equipment until only the monitor is plugged in.
If this works restore the equipment one by one until you find the fault.
Try this order
monitor
fans
hard drives
If it does not work with just the monitor it is either a faulty power supply or a faulty motherboard.
The Power supply is a the cheapest one to buy, to find out which is faulty.