Could be many numerous factors. Hardware or software related. I would start with the possible software related issue and back up all of your personal files and reinstall the operating system. If it continues to crash, you may have an issue with your memory (if you have added any usually) or your motherboard. Contact your manufacturer or retailer for assistance in repair.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix desktop pcs.