Computer Diagnostics

The first goal of any computer diagnostic or PC repair is to determine if you have a hardware or software problem.

Computer hardware malfunctions can cause software errors, crashes and blue screens so don’t skip the hardware diagnostics. Hardware trumps software. Do this first and your computer repair job will be much less frustrating.

The instructions that follow assume that you are familiar with the basics of computer operation and computer maintenance. You don’t have to be an expert but these knowledge/skills are recommended:

  • Access the computer’s BIOS configuration
  • Booting the computer to CD or USB
  • Editing the registry – (it’s not hard, just be careful)
  • Installing hard drive and adjust BIOS
  • File/folder management – move, copy, etc.
  • Uninstall applications/programs

That’s it.

Basic Hardware Diagnostic

Most hardware issues are fairly evident – no fans or signs of life, no image on the screen, mouse doesn’t work or the computer tells you that some hardware component is missing or not installed properly.

If the computer doesn’t boot or show any sign of life, start with the power supply. They can test good but still not have the juice to run the machine. Swap with a known good power supply is the best diagnostic procedure. I’ve seen power supplies test good on a meter but still not be able to fire up the computer.

For most basic hardware diagnostics, swapping the suspect problem device with a known good one or plugging the device into another computer is usually the easiest diagnostic. This will tell you if the problem is with the device or with the computer it’s plugged into.

Startup Diagnostics

At startup, the computer runs a Power On Self Test (POST). This test checks that all hardware components specified in the BIOS (CPU, RAM, video and hard drive) are present and functional. If there is problem, you’ll hear beeping diagnostic codes. Each BIOS manufacturer has there own diagnostic codes.

Once complete, the computer initiates video signal and displays the BIOS boot information. If you are not getting any video signal from the computer at this point, you have a problem with the motherboard, video card or power supply. Try a different power supply and/or video first.

If there is still no video, time for one last test. Remove all the memory (RAM) modules from the motherboard and restart. If the computer does NOT beep during POST, the motherboard is defective.

Several beeps are the computer saying “Warning, I need memory before I’ll start.” This is good.

Visual Test

Computer diagnostics should always include, first, checking the condition of the components on the motherboard and the cooling system. I have seen all brands of computers suffer from swollen or leaking capacitors on the motherboard and video cards.

Capacitors are like storage tanks (they even look like small storage tanks) that store and release electricity.

When they become defective, all kinds of strange behavior can occur depending on where they are in the circuitry of the motherboard and when the are used by the computer.

Examine all capacitors on your computer. They should be perfectly flat on top. Some have scores or creases in the tops; other have a plain cylindrical cover.

computer repair

blown capacitor

computer repair

leaking capacitor

computer repair

blown capacitors





If any of the capacitors are bulging or leaking, like these, you have a defective motherboard or video card – replace it.

Heat Diagnostics

Sudden shutdown of the computer can be caused by overheating or defective hard disk. CPU’s (Intel Pentium, AMD Athlon, etc) have a thermal shutdown mechanism that will turn off the computer if the temperature reaches the shutdown threshold.

Check for clogged CPU cooling fins or damaged fan. Sometimes the mounting bracket holding the CPU cooler to the CPU breaks. Replace cooling unit using a very thin film of Arctic Silver (or comparable) on the CPU. Be sure there is good contact between the CPU and cooler.

Carefully blow the dust out of the computer case and CPU cooler with an air compressor or canned air. Check that the CPU cooling fan turns freely.

Add-in Cards Diagnostic

If you suspect some hardware component you can’t identify is causing problems, remove all add-in cards and try booting the computer with only CPU, RAM, video, keyboard and mouse. (Of course, if you don’t have on-board video, leave the video card in).

If this resolves the error or problem, then reinstall each card one at a time and boot the computer. When the offending device is reinstalled (causing errors), you’ve identified the component that needs attention.

To further diagnose the issue:

  • Put the card in a different slot
  • Uninstall any drivers/software used by the card
  • Reinstall the driver/software for the device
  • Examine the event logs for additional information
  • Additional Computer Repair Information

By now, you may have decided that fixing your own computer is more complicated than you’d like to take on. Should you take it to a computer repair shop or have it repaired by a mobile repairman?

OK, so you’ve decided that hardware issues are not a part of your problem but you’re still having problems with your computer. It’s time to get to the software side of the problem.

Malware Diagnostics

(You know that means ALL the different kinds bad stuff, right?)

Today, most computer problems are caused by viral infestations. Infected drivers cause hardware issues, hijacked processes crash applications, rootkit modifications to the Windows kernel wreaks all kinds of havoc (except the really professional ones).

If your hardware diagnostics are good, then you’ll begin looking into software/driver issues. But remember, at this point you’re still doing diagnostics to determine the nature and extent of the problem.

During the boot process, the operating system loads legacy drivers (keyboard, mouse, beep, cdrom) early in the process.

These drivers are favorite targets of viruses because they load before the operating system security provisions kick in. This gives the infection early entry into the operating system basic elements. Infections in device drivers will sometimes cause hardware type errors – either dialog/pop-up or in the Windows event viewer.

Next, we’ll use the Windows Task Manager and Event Viewer to get information about possible causes of the computer problems.

Or, if you want to jump right in, you’ll use some advance diagnostic software to dig deeper into the operating system – rootkit diagnostics.