I'd say try the process of elimination everyone else is mentioning. Usually what is crashing the computer is also definitive. Also, what kind of crash is it? Is it a freeze? Is it a BSOD? Does the screen flicker, go black, or freeze? Does the audio go crazy when it crashes? Does Windows display an error before it crashes? It's not only a process of elimination on the hardware side, but on the software side as well.
You seem to be very vague. Almost as if you wanted to be on purpose to get rid of the hassle. You want us to validate your desire to return the parts for no good reason. I work for an electronics retailer, and user error is a huge part of our return base. In my opinion, if you don't know how to use it, or assemble it, or configure it, or afford to part with the money for people to do all that for you, you shouldn't buy it. Just so you know, when you say something like you want Amazon to "sort it out" it comes across like you're mad at Amazon, while the only person to blame is you, or the manufacturer who you don't want to hassle with. You lose out on a good experience, Amazon loses money for your ignorance, they send out the part to the manufacturer to run tests on, it goes back to Amazon to sell as Open Box which they'll likely lose money on a second time around. It's not fair or beneficial to anyone once it gets to the point you're at. The best thing to do is be civil and clear with everyone trying to help you, whether it's Us, the Manufacturer, or Amazon.