I had a pre-made lenovo, but I was getting some blue screen errors and some windows that were randomly freezing. So I started switching out some hardware. I put in a new motherboard, new power supply, new CPU fan, but the chip (i7 4770), ram, video card (nvidia gtx650), hard drive are the same. I reformatted with windows 7, and have since updated all the drivers... But I am still having my windows freeze up randomly. What could be the issue?