Monitor not coming on when starting g4 powermac

I saw it working with a monitor yesterday now it is black. I tried another monitor and it said the mac was in standby mode - press any key or move the mouse. I did this but it's still switched off. How can I get my mac to come alive? is there a master reset or something?

I am completely new to macs.
thanks,
Jules

Check your power connections. Does anything at all happen when you press the power button? Fan start (at least momentarily)?; power button illuminate? It is possible that you may need to replace the pram battery (½AA, 3.6v).