Hey,
That sucks, sorry to hear it. I would first ensure that all of your connections are good (mainly CPU 12V, Main-board connector, and PCI-E 6-pin power), and that you have an adequate enough power supply. Also ensure that when you mounted the board in the case; you put the case mounting-point screw / backpane dividers in the correct areas (make sure one is not in the wrong place shorting the back of the board to the case backpane). It unfortunately sound to me like a board issue, but try out those things first, and make sure everything is seated correctly into it's appropriate slots; as well as the CPU, and especially the RAM must be popped in fully (re-seat it, and try using just one stick for the moment... if that stick doesn't work try another stick by itself to make sure it's not the RAM).
An easy way to test to see if the board is dead is to ensure that you have a speaker plugged into the board (near Front-pin-headers), or that one is integrated into the board, and then remove all RAM from the motherboard. If you get no beeps at all then generally thew motherboard is dead.
Post back with what you find without buying new parts; once we have that hopefully we can make an educated guess to what part is failing, if any.
God speed!