How Can I Tell if My CPU Is Bad?

By Jeff Grundy

Troubleshooting CPU problems may take only a few minutes or it could take many hours.
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Because the CPU does all of the heavy lifting when it comes to performing calculations and operations, it is the heart of any computer system. Therefore, it can be difficult, or impossible, to do anything with your PC when the CPU is defective or not working like it should. In some cases, detecting a bad CPU might take only a few seconds. Other times, though, diagnosing a faulty CPU may take considerable time and require the use of external hardware and software resources.

Eliminating Other Possibilities

CPUs that fail altogether are rare. Therefore, before you try to determine if your system's CPU is defective, you should rule out other possible hardware failures first. If the computer won't boot or turn on at all, disconnect all hard drives, optical drives and other hardware cables inside the case. Also, remove any add-on cards, such as NIC cards or controller cards, inserted into the motherboard. Try to turn on the computer with only the power supply and video cable connected. If the computer boots, reconnect or replace the other hardware components one by one until the system fails. If the system fails to boot, remove or disconnect the device and try again. If the computer won't boot with only the PSU and monitor connected, try to locate another power supply and video card to try with the motherboard. Finally, if that fails, insert the CPU into another motherboard and see if it boots that system. Using the trial-and-error method takes a considerable amount of time, but is usually the surest way to find the hardware failure.

The Keyboard Test

Even if your monitor does not display an image when attempting to boot your computer, the keyboard may be able to tell you if your motherboard and CPU are at least functioning well enough to pass the basic POST test. If after attempting to boot the computer, the monitor does not display the initial POST screen or company logo, shut down the PC and restart it. As soon as you press the Power button, look at the three LED lights above the number pad on the keyboard. If the "NumLock," "Scroll Lock" and "Caps Lock" LEDs all flash briefly, chances are good that the motherboard and CPU are getting power and functional. Try re-seating the video card and memory modules, and then try to boot the computer again.

Heat Problems

One of the most common problems with processors is heat. While a CPU can work for many years without problems, the same is not usually true of the fan that cools the processor. With occasional cleaning to remove dirt, dust and grime, a CPU cooling fan may last a few years. If the fan becomes too dirty, though, the blades may not spin fast enough, or the cooling device may fail altogether. If your computer boots normally, but then freezes or shuts down after a few minutes, check the CPU fan. Clean the CPU fan, or if necessary replace it, before rebooting the computer. To make sure that the CPU cools down completely, leave the computer off for a couple of hours before trying to reboot it. Alternatively, remove the CPU from the motherboard, place it inside an anti-static bag and place it in the freezer for an hour or so. As long as no moisture can get to the CPU, the cold air in the freezer will not affect the processor.

General Protection Faults

Many hardware problems can cause BSODs (Blue Screens of Death,) which always result in system lockups or shutdowns. The most common causes of BSODs are General Protection Faults, or GPFs. By its definition, a GPF indicates that the processor has failed in some way. However, in most cases, the failure is not the processor itself, but merely a failure of the CPU to receive data from the bus or another hardware component. Nevertheless, if you see "Stack Overflow" or "Divide by Zero" messages in GPF or BSOD screens, chances are, the processor might be faulty, too hot or overclocked too much in the BIOS. If you do overclock your processor, reduce the bus speed and multiplier for the CPU in the BIOS to determine if this caused your system freezes or BSODs. If you do not overclock your CPU, try disabling the external cache for the processor in the BIOS. If disabling the cache solves the problem, boot the system a couple of times, and then re-enable the cache. If the problem returns, check the motherboard as well for bulged or popped capacitors.

Software Testing

If you overclock your processor, it may seem to run fine most of the time. Other times, the system may seem to crash randomly and for no reason at all. In most cases, simply returning the BIOS processor settings to their defaults will tell you if this is indeed the problem. However, if you are sure the processor is running at a suitable clock speed, are relatively sure that the cooling fan is okay and don’t suspect other motherboard or power-related problems, software tests may be able to help you find the problem. Software applications such as Hot CPU Tester Pro, BurnIn64 and PC Diag are excellent for stress testing the CPU and other critical components (links in Resources). The applications provide many types of CPU-specific tests as well as burn-in tests, which simulate heavy usage for extended periods. If there is a problem with the CPU, stress testing should produce errors relatively quickly. Nevertheless, you may need to burn-in the system for 24 hours or more to determine for sure whether or not the processor is functioning properly and reliably.