This is probably a faulty power supply shorting out and then recieving power again. I would definetly buy a new one and then plug this up before trying to turn your PC on again as it could do more damage.
You can buy them from most computer shops and people usually go for 450-600 watt ones now depending on the computer hardware.
To be safe, i'd go for a 500 watt power supply.
They are reletivly easy to set up too, and you just need to plug the cables back onto the devices again and plug the main power cord back into the motherboard. A good power supply should contain enough molex power supplies for this
Hope this helps