Page 1 901 Hardware and Network Troubleshooting Study Guide for the CompTIA® A+ exam

How to Prepare for the Hardware and Network Troubleshooting Questions on the CompTIA A+ 901 Test

General Information

It’s not enough to know the computer components and networking basics. You also have to know what to do when something goes wrong. This is called troubleshooting and it is a big part of IT work. About 28% of the CompTIA A+ test is related to troubleshooting of hardware and networks. Here is an outline of the things you’ll need to know. Be sure to find out all the details in a good IT textbook or other resource.

Keep in mind, as you study, that all of the questions about troubleshooting and the following material will begin with a given situation. You will be asked to analyze that situation and choose the best response to the question about it from the answer choices.

Motherboards, RAM, CPU, and Power

For this section, you should be able to troubleshoot issues with motherboards, RAM, CPU, and power. You also need to be able to use the correct tools when troubleshooting this hardware.

Common Symptoms

You should know the common causes of these various symptoms associated with problems of computer hardware.

  • unexpected shutdowns: These can be caused by hardware that’s failing or by adding new hardware that’s incompatible.

  • system lockups: They can be caused by something freezing up the operating system, such as a bad system or application process, or by using old software or driver versions. Maxed out RAM can also cause a lockup.

  • POST code beeps: Errors in the Power On Self test are associated with hardware components required to successfully boot the system. The cause of these could be problems with BIOS configuration or hardware.

  • blank screen on boot-up: BIOS or CMOS battery issues can be the root of this problem. Also check video signals.

  • BIOS time and settings resets: These indicate a problem with the BIOS CMOS battery.

  • attempts to boot to incorrect device: This can be caused by a problem with the boot settings within the BIOS.

  • continuous reboots: These could be related to BIOS problems or OS problems. Problems with a bad driver may also be responsible.

  • no power: Power outlet or power supply issues are usually the cause of this.

  • overheating: Problems with the fan, heat sink, dust accumulation, or something blocking the air circulation can all cause a device to overheat.

  • loud noise: This can be a result of loose hardware or issues with hard drive.

  • intermittent device failure: Hardware is usually responsible for this, in the form of a bad hardware installation, overheated components, hardware going bad, or hardware not fully connected to motherboard.

  • fans spin – no power to other devices: This can be caused by a problem with the motherboard. Also check power supply.

  • indicator lights: Indicator lights can inform you of certain problems going on with computer hardware, or tell if there is activity or power coming from a certain connection point. Consult the computer’s documentation for more information about this.

  • smoke: Smoke can indicate a blown capacitor.

  • burning smell: Again, a bad capacitor or a burned-out hardware piece can be the culprit.

  • proprietary crash screens (BSOD/pin wheel): This could be caused by faults in the OS system files.

  • distended capacitors: There could be a defective capacitor from manufacturer.


You should be familiar with the common tools used to diagnose and troubleshoot a computer. Knowing their appropriate use is also important.


This can be used to troubleshoot power issues. It can give voltage readings for AC and DC and check continuity across wiring.

Power Supply Tester

This device is used to directly test power supply voltage. It plugs in directly to the power supply and gives a reading of the voltages coming out of it.

Loopback Plugs

These are used to test physical connections on your computer. The connections can be serial or ethernet/network. These plugs are specially wired to transmit and receive a signal to themselves, simulating an active connection.


This is used to provide status messages while the system is booting. It can be useful on motherboards that do not have an LCD display built in for this purpose or to diagnose boot issues.

Hard Drives and RAID Arrays

For some questions, you should be able to troubleshoot issues with hard drives and RAID arrays. You also need to be able to use the correct tools when troubleshooting this hardware.

Common Symptoms

You should know the common causes of these various symptoms associated with problems of hard drives and RAID technology.

  • read/write failure: This indicates a dying hard drive and could happen if the read/write head crashes.

  • slow performance: This can indicate that a drive has already failed or that there are errors on the drive files. There may also be issues with virtual memory.

  • loud clicking noise: This can be caused by a mechanical failure within the drive itself.

  • failure to boot: This failure could be a hardware or software issue, depending on what stage the boot process gets to before it happens. Check for BIOS settings for removable devices such as USB drive. Cables and connectors can also cause the problem,

  • drive not recognized: Typically, this indicates a hardware issue with one of the drives. This could be a failed component, a data corruption issue, or an error in BIOS settings.

  • OS not found: This message indicates a software issue with loading the operating system.

  • RAID not found: This problem could be caused by issues with the RAID controller or the management software.

  • RAID stops working: This can happen in any RAID array that does not mirror data. It is usually caused by one of the drives failing.

  • proprietary crash screens (BSOD/pin wheel): This is known as the “blue screen of death.” On Windows, this is a stop error, and on Apple, you will get a continuous pinwheel on the screen. This typically indicates a fatal failure, such as a CPU dying or a burned-out part.

  • S.M.A.R.T. errors: This stands for Self Monitoring Analysis and Reporting Technology, and it includes multiple error categories known as SMART statistics. These can proactively see issues before a drive fails completely.


You should be familiar with the common tools used to diagnose and troubleshoot hard drives and RAID arrays.

  • screwdriver: A good general screwdriver set is needed to aid in removing components inside your computer case, as well as a set of torx screwdrivers.

  • external enclosures: These provide a place in which to place hard drives after you’ve removed them from your computer. It allows you to connect through USB for accessing or recovering files.

  • CHKDSK: This command is used to perform a check on the file system. If any errors are found, it can also correct them for you.

  • FORMAT: This command is used on new partitions to install the file system.

  • file recovery software: Special software that can be used to recover lost data, this is useful if you format a drive accidentally, erasing your data, or if some files have been deleted and you need to recover them.

  • bootrec: This tool, located in System Recovery Tools, allows you to repair boot files, such as the Master Boot Record, used in loading an operating system. It is helpful in isolating trouble with startup issues.

  • diskpart: Partitioning your hard drive within Windows is possible using this tool. It can also help manage volumes and disks.

  • defragmentation tool: This allows you to defragment your hard drive, which can improve access times to files. It helps place files as continuous pieces of information, instead of having that information broken up in several places. Solid-state drives should never be defragmented.