As a quick test, take another power supply and hook it up to the board, if it works then you know it's the Power Supply. If you recently hooked up a new device and now you have this issue, it may be because the power supply does not have enough juice to power the system, if that is not the case try the next thought.
Narrow it down to figure out what is broken. First remove all usb devices from the PC, hit the power button, do you see anything on the screen? If yes, one of your usb devices is crap or you have a bad usb port, if no, take all pci devices out of the board asside from the video card. If you have on board video then don't worry about it, hit the power button, do you see anything on the screen? If yes then one of your PCI devices is causing an issue, If no then do you hear any beeps? If you hear beeps refer to the mobo beep codes, if not take out the CPU, hit the power button, do you see anything on the screen? If not take the memory out, hit the power button, do you see anything on the screen? You get the idea. This will surely narrow things down so you can isolate the problem.
P.S. if the system is only two months old, then all parts should have at least a year warranty on them from the manufacturer. It does kinda sound like the mobo is bad, but test things like I outlined just to be sure you don't waste time sending a good board back, having to wait etc.. and so on.