There are lots or reasons that can cause a BSOD, both hardware and software related.
I'd start with making sure nothing is overheating, that the overclock (if any) is stable and the power supply is efficient for the particular system. Testing the memory with memtest is also a must-do. Software-wise, you can update your mainboard BIOS and install the latest WHQL drivers for all your hardware, especially the chipset, video card and sound card drivers. Then you need to update Windows and make sure you are not infected by any virus.