Check out the link in my signature. Lots of useful info on "no boot" problems, including PSU voltages to compare. The basic gist of testing the PSU is to check if your voltages are within tolerance. To do this, you'll need a multimeter. Take the black probe and touch it against anything bare metal in your case, or touch it against the back of any black wire on the P1 connector (the 20/24-pin plug). As for the red probe, touch it against the non-black colored wires and compare your voltage readings to what the voltages should be; again, these values can be found in the troubleshooting guide, so click on the link