Three Faulty PCs Before the Practical Exam
The government inter-college computer lab has ten assembled desktop computers, each with 4 GB RAM, a 500 GB hard disk and a 19-inch LED monitor, all powered through one UPS and two daisy-chained extension boards. After a thunderstorm and a sudden power cut, three machines misbehave. PC-3 gives one long and three short beeps at start-up and shows nothing on the monitor. PC-5 spins its fans and hard disk, but the screen stays blank and the keyboard lights never flash. PC-8 restarts every time the shared laser printer is switched on. The Class 10 practical examination is six days away. The lab has one spare 4 GB RAM stick, one spare VGA cable, no spare SMPS, and a repair budget of ₹6,000. The lab attendant suggests opening all ten cabinets at once and swapping parts until something works.
1. In what order should the three faulty PCs be diagnosed, and what is the most likely cause of each symptom? Justify each step.
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Diagnose from the cheapest, least risky check to the most invasive, and finish the machines needed for the practical first.
- PC-3 first. The beep pattern is a POST (power-on self-test) error, so the machine stops before any operating system loads. One long and three short beeps commonly points to memory or video failure, but the exact meaning depends on the motherboard manual. Reseat the RAM, try the spare RAM stick, then substitute the VGA cable and check the monitor on another PC.
- PC-5 second. Fans and disk spin, but no keyboard-light flash means POST probably never completes. That supports RAM, CPU seating, motherboard or power rather than a Windows fault. Reseat RAM and power connectors; do not assume the hard disk is bad.
- PC-8 last. It restarts only when the laser printer starts, which points to a sudden current draw on a shared extension board or a failing SMPS, not to software. Test it on a different socket without the printer before buying parts.
2. The attendant wants to swap parts among all ten machines. Give a safer plan for the ₹6,000 budget and the six-day deadline.
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Swapping parts across ten machines risks damaging working computers and losing track of which part is faulty. Use a controlled plan:
- Unplug each PC, use an anti-static wrist strap or touch the bare metal case, and change one component at a time.
- Keep one working PC as a reference and label every removed part.
- Use the spare RAM and VGA cable first; these cost nothing and may repair PC-3 or PC-5.
- For PC-8, move the printer to a separate socket or the UPS and test again. If the restart continues, a 450 W SMPS typically costs ₹1,200–₹1,800, well inside ₹6,000; keep the old unit labelled.
- Do not open the other seven working PCs. Spend remaining money on a surge protector and a labelled power layout.
- Before the exam, back up practical files from all machines to a teacher's pen drive and verify that each repaired PC boots, displays, prints and saves a test file. Record the work in the lab register.
3. Why is the fact that PC-5's keyboard lights never flash significant, and what does it rule out?
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On most desktop PCs, the keyboard LEDs flash once during POST as the keyboard controller is initialised. If the fans and disk spin but there is no LED flash and no display, the system is probably failing before or during POST, so it has not reached the stage of loading an operating system. That makes a corrupted Windows installation, a virus or a bad user profile unlikely to be the primary cause; a working PC with those problems would still show POST activity and usually a display.
The evidence points towards the power supply, RAM seating, CPU or motherboard. The monitor and cable still need checking, because a dead monitor can look like a POST failure. Test the monitor on a known working PC, then reseat RAM and power connectors. Only after those checks should the SMPS be suspected. This reasoning prevents the common mistake of reinstalling Windows when the hardware has not even completed its self-test.