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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting The System Overall ]

Troubleshooting System Instability, Reboots and Crashes

Explanation: The system is booting up and starting to work correctly, but on occasion it either reboots without warning, or seizes hard (no mouse or keyboard response, and a reboot is necessary). These symptoms occur over a period of time.

Diagnosis: This is, unfortunately, one of the most difficult of all problems to troubleshoot on the PC. The reason is twofold: first, these problems are usually intermittent, and therefore hard to pin down to any particular cause, and second, there is a really large variety of problems that can cause this sort of behavior. It is necessary to narrow done the specific circumstances in order to have a better chance at finding the problem. See below for possible causes, which are listed with the recommendations to possibly solve them.

Recommendation: Follow the questions and suggestions below to try to identify the cause of the problem:

  • Did you remember to scan the system for viruses? Lockups and instability are "classic" virus infection behavior.
  • Make sure that you disable all power management options in the BIOS setup program. They can cause spurious behavior, particularly on some motherboards.
  • Are you getting error messages when the problem occurs? If so, try to find the error message here.
  • Are you experiencing this problem only when running a specific application program? If so, it may be the application itself that is causing the problem.
  • If the problem occurs only when you use a specific peripheral, such as a mouse or modem, there are three typical possible causes specific to this situation. First, there may be a problem with the particular peripheral you are trying to use. Second, you may have a resource conflict that is causing the system to lock up when you try to have two devices access the same resources. Finally, there may be a driver problem with the device, if it is something that uses a driver in the operating system you are using. Look in this section for specific troubleshooting information for various devices. Use the resource conflict troubleshooter.
  • If the problem occurs only when the system is warmed up (meaning not within the first few minutes that the PC is turned on, but only afterwards), or if the problem occurs only when the room where the PC is located is hot, it is likely that the problem is hardware-related and probably something to do with the motherboard, processor or another system component that is running too hot. I would suggest that you refer to this section, which describes checking for overheating components inside the box, and follow the recommendations there.
  • Are you running a VESA local bus video card on a motherboard that supports both VESA and PCI? If so, you should realize that this combination has been known in the past to cause instability. Try replacing the VESA video card with an inexpensive PCI video card and see if the problem goes away.
  • If you have just bought or assembled this PC, or performed an upgrade to it, check this list of possible candidate causes of system problems that is related to new installs.
  • If the problem occurs when you lean against the system box or when you put the monitor on top of it, try here.
  • If you are running Windows 3.x, does the problem seem to occur after using the system for a long time, or if you use a large number of applications simultaneously? If so, go to the Program Manager, click "Help", then "About Program Manager". Check the number listed for system resources. If it is below about 20-30%, that may be the cause of your problem. Try rebooting and checking the value, to see if it increases, and see if the system runs better. I recommend rebooting Windows 3.x daily if it is heavily used. Check this section for ideas on dealing with system resources under Windows 3.x.
  • If the problem is occurring under Windows 3.x or Windows 95, try using just DOS software for a while and see if the problem goes away. If it does, then you may have a problem with your installation of Windows, although it could still be a hardware problem (Windows is more sensitive to these than DOS is).
  • If you have a network card, check your network settings. Sometimes the built-in networking in Windows will spend a great deal of time "looking" for a network when one is not there, which causes the system to lock up and then unlock periodically. If you are using TCP/IP or another protocol, try disabling the protocol and see if that fixes the problem. You may need to contact your network card manufacturer or Microsoft for more assistance if this is the case.
  • If you have recently changed any BIOS settings--especially those that control system timing--and the problem has started since around that time, try changing the BIOS setting back to the previous value, or resetting the BIOS settings to low-risk defaults to see if the problem goes away. You may also want to follow this procedure to set your key BIOS settings to safe values.
  • Scan the hard disk for file system corruption and check for bad sectors as well.
  • Drivers can cause seemingly random glitches and lockups if they are poorly written, especially the video driver. Try running the system with a "slow but sure" default driver or a different version obtained from the manufacturer. Sound card drivers can also be touchy in this way. Try turning off hardware acceleration in Windows 95 by selecting System in the Control Panel, then selecting the Performance tab and clicking "Graphics".
  • Unreliable power can cause all sorts of strange system problems. A common problem is having the input voltage selection on the back of the power supply set to 220V when it should be 110V. If possible, try running the system off a UPS and see if the problem goes away. If practical, try swapping in a new power supply. If you notice the lights dim briefly at around the time that this problem occurs, this is a power problem.
  • Try using less aggressive BIOS settings for items such as memory timing and hard disk timing. For example, set the BIOS memory access settings to the slowest possible. Disable any performance-enhancing BIOS options (such as those described here) to see if the instability goes away. Try running the hard disks at a lower PIO mode to see if IDE timing might be causing the problem.
  • Under Windows 95, make sure you have a sufficiently large swap file enabled. A too-small swap file may cause problems. If you have been tinkering with the virtual memory settings this may be the cause of the problem. See this section for ideas on swap file size optimization.
  • Check for resource conflicts.
  • Troubleshoot the processor.
  • Troubleshoot the system memory. Memory problems are a frequent cause of crashes and other spurious behavior.
  • Troubleshoot the motherboard.

Next: Troubleshooting System Slowdowns

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