My computer keeps freezing completely

Hello!
I've only had my computer for about a month and a half, and I've noticed that recently the computer just freezes randomly, and the only way to make it work again is if I turn it off from the mains, and turn the computer on again.
I am not too sure why this happens, as this computer is new, it has no viruses, and was a very expensive computer with a good graphics card and specs.
Every part of the computer was manually custom built for me by the company who sold it, so I believe that everything has been set up correctly in the bios settings.
I cannot think of any reason for this to happen, as it does have a superior cooling fan so it cannot be that it is heating up too much.
Does anybody have any idea why this keeps happening, or even better - how am I supposed to fix this! I hate loosing my work.
 
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