Please help.

[xhanababiix]

For the past week or so, my laptop keeps crashing. It completely shuts down every half an hour or so without any warning. When I turn it back on, it just starts as normal, then crashes again after a little while. I have no idea why, I havent downloaded anything recently.
I'm not very knowledgeable about computers, so if this could be explained to me as simply as possible I would greatly appreciate it.
Thank you

[quaxo]

Laptop make and model? Operating system?

What do you mean it crashes? Does the system completely lock up? Do you see a blue screen? Does this happen when playing games or just generally any time? Need a bit more detail on what it's doing.

[Mulreay]

For the past week or so, my laptop keeps crashing. It completely shuts down every half an hour or so without any warning. When I turn it back on, it just starts as normal, then crashes again after a little while. I have no idea why, I havent downloaded anything recently.
I'm not very knowledgeable about computers, so if this could be explained to me as simply as possible I would greatly appreciate it.
Thank you

You could be over heating. where is your laptop situated? Is it on a flat hard surface or a soft one? Unfortunately because we are now in Summer you need to take greater care when it comes to protecting your laptop. It may sound strange but I have created a bench for my laptop to lift it off a surface. Next time it shuts down run your hand underneath and feel the temp of the bottom. I bet it's really hot.

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[Quantos]

You should also blow out the cooling fans and heat sink, it should say in your manual how to do that.

[Mulreay]

You should also blow out the cooling fans and heat sink, it should say in your manual how to do that.

And that 

[xhanababiix]

You could be over heating. where is your laptop situated? Is it on a flat hard surface or a soft one? Unfortunately because we are now in Summer you need to take greater care when it comes to protecting your laptop. It may sound strange but I have created a bench for my laptop to lift it off a surface. Next time it shuts down run your hand underneath and feel the temp of the bottom. I bet it's really hot.

Usually have the laptop on my lap or a soft surface. I didn't even think about the weather, but you could be right seeing as it has only happened over the past week. The crashing usually occurs when I'm playing games but it has occured other times, and I find that underneath the laptop is very hot. What do you recommend?
There is no blue screen or any warning, it just turns off completely.

[Quantos]

You could also use a notebook cooling pad, the more fans in it the better.

[Mulreay]

Usually have the laptop on my lap or a soft surface. I didn't even think about the weather, but you could be right seeing as it has only happened over the past week. The crashing usually occurs when I'm playing games but it has occured other times, and I find that underneath the laptop is very hot. What do you recommend?
There is no blue screen or any warning, it just turns off completely.

It's overheating mate. Your laptop will automatically shut off (no warning) when it reaches a critical temp. As Quantos suggested get a cooling pad but don't leave your laptop on a soft surface. All the fans blow out of the bottom so soft surfaces e.g sofa's or your bed will block up the vents and cause overheat. My laptop has shut down a fair few times because of this, just be thankful that your laptop does shut down or you could look at a burnt out laptop.