First check your psu if it is good. To check psu you can test it on another system or paper clip method.
To use paper clip method, make the clip U shape and put one end green wire and another end to black wire in 20/24 pin power connector of your psu. You cant connect a fan or dvd rom to psu. Then power up and see if psu fan or connected fan spnning or dvd rom led blinking. If psu is dead then nothing will happen.
If psu is alright, then it cloud be your mobo which is dead.