Power on but screen monitor still no respon

When you clear the BIOS (CMOS reset) you have to set the date and drive priority for boot. You need to enter the BIOS (settings menu) to do this.

If you hear the CPU fan turn on that doesn't mean the CPU itself is working. It can be only that the motherboard is getting power. Check all your connections such as monitor and peripherals and re-connect them. If you still don't get P.O.S.T. or ANY letters or boot options on your screen then your CPU is dead. (unless your monitor is bad)
Another easy diagnostic is using your ears. For example the pitch sound of the fan in some motherboards tends to lower and then increase because it's reading of the hard drive. This means your CPU is ok but either your graphics connection is bad or your monitor is.

The monitor works on another computer?

This is a problem coming from your signal cable(cable from system unit to monitor).
All you have to do is to change it.
If it still doesn't work, you have to change your monitor

When you
When you power up your computer and the monitor screen remains dark, the problem can be either be associated with your monitor, or your computer power supply/video card/motherboard or CPU. Perform the following tests to isolate the problem to either the monitor or the computer.
1. Turn off you PC and monitor. Then verify that the 15 pin video data cable connectors are fully inserted into their receptacles on the rear of your PC and on the rear of the monitor and they are tightened down. (on some monitors the data cable is hard-wired to the monitor). Then make sure that both your monitor power cable is securely plugged into a working AC power receptacle. (You can temporarily plug a lamp into your AC power receptacle to make sure you have a good source of AC power).
3. Turn on the power switch on your monitor. The amber colored LED on your monitor should come on. Then turn on your PC. The fans in your PC start to run and continue to run and the LED on your monitor should change from amber to green.
???
Now if the monitor led remains amber and the screen stays dark you either have a bad monitor or a problem with your video card, motherboard or processor.. Try using a different monitor. If that doesn't solve the problem, you need to have a PC technician test your computer.
If you have any additional questions contact me by clicking on the "Add a comment" link located under your problem description on FixYa. Also, if you believe that this information was helpful to you, please return to the FixYa website and rate my response to your question.
Best regards,
Yavacotech

EVEN THOUGH FAN RUNNING WE CANNOT SAY POPOWER SUPPLY IS OK. SO CHANGE POWER SUPPLY AND MEMORY .. AND TEST IT

Solid Amber Power LED is indicative of a Motherboard failure. Replace the motherboard.

The GX280 is one of many motherboards made during that time period that may have had capacitors that could fail due to a manufacturing defect if the capacitor. Check the capacitors on the motherboard to see if the tops are popped (there is a X engraved across the top of each capacitor, it the X is open, then the capacitor is bad.)

Try to reset the CMOS on the motherboard.

Try this... to see if your video card is bad...
Connect your laptop to an external monitor and press the Function key plus F5 on the laptop... if your OS shows up on the monitor screen, then you have a bad video card...

If its not the video, Bad Ram might be the cause.
And worst case.. Need Motherboard replaced...

if this is a built sustem out of the box with old monitor try another monitor oddly enough some arent compatible, you can check by looking at the prong patern.