Troubleshooting is faster when you change one variable at a time. Start with the symptom, verify the simplest causes, then isolate hardware methodically instead of replacing several parts at once.
PC has no power
Check the wall outlet, surge protector, power-supply switch, motherboard 24-pin cable and CPU power cable. Verify that the case power-switch lead is connected to the correct front-panel header. If the motherboard has standby LEDs, note whether they illuminate.
Fans spin but there is no display
Confirm the monitor input and cable. If a dedicated graphics card is installed, connect the display to the graphics card unless the system is intentionally using integrated graphics. Reseat memory and the GPU, then test a minimal configuration if needed.
Memory errors or repeated restarts
Reseat the modules and verify the preferred slots. Disable an aggressive memory profile temporarily and test at default settings. If errors continue, test one module at a time in a known-good slot.
Drive detected but the system will not boot
Check the firmware boot order, operating-system boot mode and whether the expected boot device appears. If hardware was moved between systems, configuration or encryption settings may also affect startup.
High temperatures and loud fans
Check for dust, blocked filters, failed fans, an incorrectly mounted cooler or an unplugged pump/fan cable. Confirm thermal compound and mounting pressure only if the cooler installation is suspect. Use realistic load testing and manufacturer temperature guidance.
Crashes under load
Instability can come from overheating, memory errors, power issues, driver problems, storage errors or aggressive overclocking. Return hardware to default settings, update essential drivers and firmware where appropriate, and test each subsystem separately.
Motherboard diagnostic lights and POST codes
Many boards include CPU, DRAM, VGA and boot indicator LEDs, while some provide a numeric POST display. These indicators can narrow the search, but their meaning depends on the exact motherboard, so use its manual rather than a generic code list.
When data matters more than the computer
If a storage device contains irreplaceable data and is clicking, disappearing or repeatedly corrupting files, stop unnecessary testing and writes. The priority may be data recovery, not making the old drive boot one more time. Review the storage and backup guide for prevention and recovery planning.
When to seek professional help
Stop if the work involves damaged power connections, liquid damage, a power-supply enclosure, burnt components or anything you are not comfortable diagnosing safely. A qualified repair technician can test with known-good parts and equipment that most home users do not keep on hand.