I would expect it's heating related. I repaired my mother's new computer because of heat related issues. The GPU (graphics processing unit - ie the built in graphics card) was overheating. The heatsink that HP installed wasn't enough. I had to mount an old cpu heatsink with fan to it to fix.
Same symptoms that you described.
An easy way to tell if it's related is to download Speedfan. This program is free and will allow you to check the speed the fans are running and also provide you with the current temperature for all the heat sensors within the computer (including CPU, GPU, etc).
You can download it here: You are not allowed to view links.
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LoginAnother possible cause is bad ram as others have mentioned. You can run a memory test to see if there's a problem with the memory installed.
Hope this helps,
Shannon