Also try resetting the cmos either by jumper or removing the battery for 1-5 mins do this with the computer unplugged then re-install the battery. God knows how many times this has worked.
Another thing you can try, I had an instance last week where I set the jumper to auto detect but no post so I set the actuall FSB for the cpu with the jumpers once I done this it booted right up. don't ask me why auto should have worked but did not. Setting the jumper to the cpu recommended FSB did the trick.
Also if you get a beep during power up decipher your beep code
here before doing anything else. Usually it is a simple problem you can workout, particulary with a new build. Most new builds are an error on the builders part during the assembly process or the incorporation of incompatible parts. Very seldom when using new quality parts is there a problem with the actual part. If you are at your wits end and you suspect you have a faulty part you can have the indivual part tested at a local computer store, or post your problem in the forum and maybe one of the members can help you further.