Check your cables. Make sure you have the 20/24 pin AND the 4/8 pin CPU power and that all your drives are powered. Remove and reseat them all to be sure. A minimum of 4 wires coming off the PSU should be plugged in, 20/24 pin, 4/8 pin, HDD and Optical drive.
Check the seating of the graphics card by removing and refitting it as it is common to dislodge it when changing the power supply also try the same with the memory. Another common mistake is to forget to fit the 4 pin connector. If this does not work can you try the old power supply again?