Problem with maintaining power to monitor

[hawthorn]

On one of the computers I have got when you turn it on you hear the monitor click to turn on when the computer is switched on like it always has and then recently it has clicked again before anything comes on screen and turns the power back off to the monitor.  I thought it may be that the monitor has died, but it appears that it isn't that.  I tried plugging in a different monitor which I know works but the same thing happens, so it must be something inside the box of the computer and I have no idea what part of the computer other than the monitor would make the monitor not operate.  What part of the computer would cause something like this to happen?

The beeps, fan starting up etc with the case of the computer all happen as before, but just the monitor gets no power for more than 1 second before dropping out.

Thanks for any help you can offer.

[Broni]

Welcome aboard

Try another monitor cable.

[soybean]

I tried plugging in a different monitor which I know works but the same thing happens, so it must be something inside the box of the computer and I have no idea what part of the computer other than the monitor would make the monitor not operate.  What part of the computer would cause something like this to happen?

Have you tried connecting the first monitor into another computer to see how it works?   Does this computer have onboard video or a video card?