When I open the system, its normally functioning. But after a few minutes the monitor power off and on! But the system is normally running, only the monitor has malfunctioned! How do I fixed this.? Somebody help me.. is the monitor has a problem?

Unless you are trained in electronics... and have the test equipment, AND schematics. You aren't going to be able to fix this yourself. If you did, you wouldn't be asking us this question.

Its time to buy a new monitor. There are dangerous voltages inside the unit that can kill you.

If your monitor is an LED flatscreen, try checking where the power plug goes into the back of the monitor. Since they almost always plug in upwards, they have a tendency to work themselves out if moved around. Also check where the plug goes into the wall or power strip and see if its nice and tight, if you use a power strip and it were loose at the wall, I suspect other things would be interupted as well. I had a monitor that would show the little green light which meant it was on but would not show a post screen. When I fully seated the loose power in the back the post screen came back. For some reason it had enough power to light the little light but not the back light.

But, my monitor is not a flat screen type. It is also like a TV screen.. old modern of a computer monitor.. but thanks for your info. I tried to apply that...

You might want to check the outlet your plugging it into. Are the plugs prongs clean and fit snuggly into the wall socket?