Have you checked your cables, and made certain they are connected? Post back, and we will go step by step, as you have made no effort to let us in on any details, such as what you have checked or tried!
Please do not reload the OS because of issues such as these. Take out all of the RAm and leave only the Hardrive connected. Does it boot to error, or beep? If it DOES NOT beep, then the Motherboard is bad!