PowerMac G4 booting but not showing.

I was recently given an PowerMac G4, everything is in and it is in working order apart from when I boot the PowerMac it doesn't show up on my VGA LCD screen. I'm not sure if it’s the PowerMac or the screen. And another question, if the PowerMac doesn't have an operating system would it show on the screen?

If the Powermac was lacking an OS, it would display a question mark on the screen on startup.

I'd try a monitor of which you are sure it works.

The monitor seems to work fine with a Window's computer. But I have no idea what's going on with the Mac. Also the inside of the PowerMac G4 is slightly dirty, should I clean the video card? Or what?

Can anyone help?

Your video card might be the issue, although I don't think that merely cleaning is going to solve it.

Theres no harm in trying, as long as you don't throw it in a bucket of water;D
Try blowing it with a can of compressed air, if you happen to have one.
Did you check the monitor with the same cable?

No luck, yes I did try the monitor with the same cable and it worked perfectly with Window's. I have no idea what is going on.

It could also be your logicboard as stated here.