First of all, post the make and model of the system or the make and model of the individual components including power supply, motherboard, cpu, memory and video.
Be a little more specific as to the symptoms: Does it power up? Any error messages? What was the last thing you were doing when it crashed? Did you just install any new hardware or software?
Be a little more specific as to the symptoms: Does it power up? Any error messages? What was the last thing you were doing when it crashed? Did you just install any new hardware or software?