Advent laptop won't turn on (Boot-up keeps cutting out)?

When I press the power on to turn it on the blue light comes on, then after about 10 seconds all power cuts out and it turns itself off. No activity on the screen. I've taken the battery out and tried with just the cable. Nothing. Tried removing battery and holding power on for 20 secs. Nothing. No signs of life on the screen. Please help!!!!!