Hardware and Network Troubleshooting · Topic 2 of 7
Troubleshooting Motherboard, RAM, CPU and Power
Diagnose computers that will not start, beep, shut down, overheat or lose the clock, and link each symptom to the board, memory, processor or power supply.
- 5 min
- No power at all points to the outlet, cable, PSU or front panel switch.
- Beep codes come from POST, and the pattern means a specific fault in the manual.
- Random restarts often come from heat, a weak PSU or bad RAM.
What it is
Many faults come from the core parts of a computer: the motherboard, the memory modules (RAM), the central processing unit (CPU) and the power supply unit (PSU). Their symptoms overlap, so you learn the patterns and test in a sensible order.
The skill is to read the symptom, form a theory and test the cheapest and safest cause first.
How it works
Symptoms and likely causes
| Symptom | Likely causes |
|---|---|
| No power at all, no lights or fans | Power cable or outlet, switch on the PSU, failed PSU, loose front panel power lead |
| Powers on but no display | Seating of RAM or graphics card, display cable, failed RAM, CPU not seated |
| Beep codes at start | The power on self test (POST) found a fault; the pattern points to RAM, video or the board. Check the maker's manual |
| Random shutdowns or restarts | Overheating, failing PSU, bad RAM, dust |
| Blue screen on Windows, or a spinning wheel on macOS | Bad RAM, failing drive, driver fault, overheating. These are called proprietary crash screens |
| Burning smell or smoke | Failed PSU or electrical part; switch off at once |
| Distended or leaking capacitors | Failing board; replace the board |
| Date and time reset | Dead CMOS battery |
| Fans loud or constant | Dust, hot CPU, blocked airflow, failed fan |
| Slow performance, throttling | Overheating CPU, not enough RAM, dust |
| Lights or fans spin and stop | PSU not delivering enough power, short circuit, bad board |
The complementary metal oxide semiconductor (CMOS) battery keeps the clock and firmware settings, so a clock that keeps resetting points to a worn battery. It is a small coin cell that is cheap to replace.
Application crashes. A program that closes or freezes while other software runs fine is often a software fault, so update or reinstall it first. If several programs crash, or crashes come with restarts, suspect hardware: bad RAM, overheating, a failing drive, an overclocked CPU, a driver fault or unstable power. Run a memory test first, then check temperatures, drive health and any overclock setting.
Power and the PSU
Check the outlet, the cable and the switch at the back. Try a different cable or outlet.
Use a PSU tester or a multimeter to check output voltages. If the unit fails or is unstable, replace it with the same or higher rating.
Never open a PSU, and switch off and unplug the computer before touching internal parts, because capacitors can hold a dangerous charge.
A PSU that is too small for the parts may work at idle and shut down under load, such as during games.
RAM problems
Faulty or badly seated RAM causes failures to start, beeps, restarts and crash screens. Reseat each module, try one module at a time and try different slots. Run a memory test tool from the operating system or firmware if available.
Mixed memory types or speeds can cause errors. Memory must match the board's supported type.
CPU and heat
Heat is a leading cause of random restarts and slow performance. A CPU shuts down or slows (throttles) itself to avoid damage.
Check these items:
- Is the CPU fan spinning, and is it plugged into the correct header?
- Are the heat sink and vents clean?
- Is the heat sink seated, with thermal paste in place?
- Is airflow through the case clear?
Clean dust with compressed air, with the computer off. Hold fans still while cleaning so they do not spin too fast.
The motherboard
Board faults are the hardest to prove, so rule out cheaper causes first. Look for bulging capacitors, scorched spots and bent socket pins. Disconnect all non essential parts and add them back one by one to find a shorted part.
Update firmware if the symptoms started after a hardware change, and reset the firmware to defaults if a setting might be the cause.
Indicator lights and beeps
Many boards have small lights or a code display that show the stage where start up stopped. Look up the code in the manual, since each maker uses its own patterns.
A step by step approach
Reseating RAM and cables, and testing with one module, costs nothing and fixes many "no display" problems.
What to remember for the exam
- No power at all points to the outlet, cable, PSU or front panel switch.
- Beep codes come from POST, and the pattern means a specific fault in the manual.
- Random restarts often come from heat, a weak PSU or bad RAM.
- A clock that resets means a dead CMOS battery.
- Blue screens and spinning wheels are proprietary crash screens, often from RAM, drive or driver issues.
- A burning smell means switch off at once.
- Distended capacitors mean a failing board.
- Reseat RAM and use known good parts to test.
Common mistakes
Replacing the motherboard first. It is the costliest and the least likely cause.
Ignoring heat. Dust and a loose heat sink produce many faults that look like other failures.
Using the wrong PSU rating. A weak unit fails under load, not at idle.
Forgetting electrostatic discharge (ESD) protection. Static damage can cause faults that appear later.
Testing several changes at once. You cannot tell which one fixed the fault.
Check yourself
A computer's clock resets to an old date every time it is switched off. What is the likely cause?
A dead CMOS battery.
What can cause random shutdowns under heavy load?
Overheating or a power supply that cannot deliver enough power.
What is the first RAM test to try for a computer that powers on but shows nothing?
Reseat the modules, and try a single module in different slots.
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