Help pls.. Computer not starting

Hi guys facing I'm a problem with my computer.my system is not starting.after pressing the power button in cpu the monitor displays acer brand name and then it shows NO SIGNAL and turns off with a orange light till i switchoff ups.cpu will be running,dvd drive is opening and fan also works.key board is not working but mouse works with light on.ups is working fine.
Can u guys help me to get out of this prob...? Thanks in Advance!! :)