Screen goes black while using and then laptop won't power back on!

Hi,

I know there's probably a million posts like this but I can't seem to find one with the exact problem that I'm having. Every time I've used my laptop for the past 2 weeks after a certain amount of time the screen will inexplicably go black. The laptop doesn't power off as the light stays on and I can hear it running still but it does become unresponsive and the only way I can shut it down is by holding the power button til it shuts off. Once the laptop is shut down it won't come back on no matter how many times I press the power button. After a certain amount of time the laptop usually powers up again by itself or if I leave it closed for a few hours I find I can turn it on again no problem but ultimately the screen will just does black again at some point. Last time it happened I was using the laptop for 2 hours before it blanked but the time before that I was only using it like 10 minutes. It's all very random! And I haven't a clue why it keeps happening as there's nothing wrong with the screen other than this. I think the laptop is 3 years old but it's been barely used so it shouldn't really be broken.

Can anyone explain to me what's happening? I'm completely lost!!

Thanks for your help,

Jen