Your computer's central processing unit is effectively the machine's brain. It coordinates activity between your applications, your operating system, your hardware, and everything else on which your computer relies to function. If your CPU is stuck at 100 percent usage, you'll experience dramatic slowdowns with possible crashes and freezes. Reducing CPU use demands that you take careful stock of your running applications and the state of your computer hardware.
Open your PC's Task Manager application by pressing "Ctrl-Shift-Esc." Task Manager can sometimes take a few seconds to appear. Alternatively, press "Ctrl-Alt-Delete" to open the Windows system menu, then click "Task Manager."
Click the "Processes" tab. Next, click "CPU" to sort the list of applications by CPU usage.
Read through the running processes to see which one is using the bulk of your CPU power. Depending on your PC setup, 100 percent CPU usage should not be occurring unless a program is updating or performing heavy calculations (Windows Updates, for example, or 3D animation software creating rendered images).
Right-click the offending application and select "End Task" to shut it down.
System and software updates can cause your CPU to spike to 100 percent usage. Task Manager will show you if Windows or your applications are performing a background update.
Viruses and other malware can also sometimes force your CPU to 100 percent usage. Perform a full system sweep to remove this as a possibility.
Aging hardware is another common cause of high CPU usage. If you’re trying to play video games, watch HD movies or run high-end software and find you're maxing out your CPU, it may be time for an upgrade.
Closing unneeded applications and focusing on one or two at a time can help reduce your CPU’s workload.
The “End Task” command may cause system instability if you use it to shut down an important system task; do not manually shut down a task if you do not know which application is using it. The “End Task” command will also dump any unsaved work you have in the application in question.
Information in this article applies to computers running Windows 8. It may vary slightly or significantly with other versions or products.