So my older acer aspire's Psu broke down, so we got a new one. The pc powered up all fans running etc, but no image was coming

I would unplug and reconnect all power supply connections. Especially paying special attention to those plugged into the graphics card and the monitor. Then, I would try again. As dumb as it sounds, I would also make sure that the monitor is plugged in and on as well.

Check the DVI/HDMI/VGA from the monitor to the graphics card or if you don't have one, the back of the computer, an dcheck that all cards are conncections from the power supply are plugged in properly. I would also replace the CR2032 battery on the motherboard while you are at it. If none of that works, message back and we can go from there.
 
@Barney I was using it, then I shut off to reset then it just wouldn't turn back on. And thanks for the info stahler ill run that to my dad because he's the tech savy one then get back to you !
 
Not sure if its worth pointing out but, when I turn everything on a box comes up on The top left of My monitor and flashes between analog and Digital about 10 times then just goes black and the light on the monitor power button blinks on and off