Laptop shuts down for no apparent reason?

You are running Vista, so that indicates that your [unknown make and model] laptop could be a few years old. That indicates that your issue COULD be one of overheating, if you have never cleaned the cooling channel out before. You see, the fan on the bottom of the laptop (that needs to be clear, so never use it on a sift surface) sucks up dirt, dust, hair as well as air. This material gathers on the leading edges of the cooling fins inside the laptop, and eventually forms a matt, similar to felt. This blocks air flow, and causes the laptop to run hot, and eventually turn off on it's own.

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Maybe your laptop is overheating, try and put it on a hardback book or on a wooden table o see if this works because it will not get hot enough to cut out my laptop used to do it all the time

perhaps your computer is overheating, attempt to positioned it on a hardback e book or on a wood table o see if this works because of the fact it won't get warm sufficient to diminish out my computer used to do it each and all of the time

may be overheating is problem. problem in fan is one of the main cause of laptop overheating go to nearest laptop repair service center and repair your laptop