Sudden crashes and blue screens can be software or hardware related. First thing to check is your memory. First download and run MemTest and if that checks out OK start thinking about other hardware such as your power supply. We know nothing about the make up of your PC and it would help if we knew your motherboard, processor, graphics, hard drive and memory details. Use something like the free version of Speccy to twll us what you have.
If all the hardware checks out then it just may be that you have a virus, some malware, a trojan perhaps. Have you run virus and malware checks? What software do you have installed to check for those things?
As you are in the Windows 8 forum I presume you have that OS installed, did that come with the machine? Have you tried to upgrade to 8.1?
Lots of questions for you but every little helps to understand how we can help you.