Black screen, Lights on

I have a HP Pavillion Entertainment. When I start the laptop the screen goes slightly grey and then remains black. The lights glow normally. The num and caps lock lights come on once and then fade (this is what i thought normally happens). I can then hear that windows starts and that my skype opens up. But the screen is still black. Anyone know what is wrong with it? and how to fix it?

The laptop is plugged in. It has had a short battery life for a year now. so it always remains plugged in.

Thanks