CPU is on but system not booting

I m karthick. I have Intel pentium dual core/quad core motherboard. my pc was working fine yesterday. From today i have turn on the cpu. cpu is running successful and moniter shows first screen in below F10 for select boot and F12 for boot menu. then after the screen will blank with top left corner underscored ( _ ) is blinking continuously. i have wait for a hour is not going after windows screen. kindly check and do thee needful.