This is a another common computer problem. However, this particular issue is a bit more serious; therefore, it needs a few diagnostic steps. In most cases this problems are caused by spyware. To avoid this problem update your anti-spyware program daily.
Having the most up to date signatures will help you avoid having a serious spyware problem. However, if you have concluded that your PC is spyware free. You should update your hardware drivers. The computer cannot communicate with various hardware components without an up to date driver. When it cannot find a driver, the CPU locks up. Also, increasing your virtual memory can also help to avoid freezes. Virtual Memory will allow to you get more use out your computer's RAM.