My cpu is working but the monitor displayed to a point and go blank?

We need to know more. I think your saying the computer boots and shows the post screen but then dosent go on and display windows, is that correct ?

Mactronix  

Sounds like you have a CRT, and it sounds like your tube is blown. You saying the monitor turns on, you get a dot of light in the middle, and it goes out?

This pretty much only happens to CRTs, never seen it with another technology, and means it's time for a new monitor.