Computer wont boot, monitors says no signal and it goes to sleep

Hello,

My Computer wont boot up then monitor says "no signal" for the cables and monitor goes to sleep ... The fan of the computer is on .. but the small light in the computer doesn't blink .. the blinking light is the sign that its booting up .. but now the light is completely off. no lights at all .. I tried checking the cables and everything plugged in and everythings fine ... I was not able to use this computer of my for days