My cpu always in stand by mode every time I boot up

Hello,

I have a problem like that when I start flug the cpu it always already on. But in standby mode when I press the cpu button it on , in normal mode,. With 2 beep sounds and there's a message in monitor press f1 then I press and violla! The monitors black screen ,after 30 sec. It will back in standby mode,.


Can you help me, or give me some tips,

Ohh forgot I unplug it all and I put it again and I clean all the dust,. Inside and out, still not boot up,

Wait from your responds,