1. Processor overheating — Modern processors generate a lot of heat. That’s why all processors require some sort of cooling element, typically a fan of some type. When the processor temperature goes over spec, the system can slow down or run erratically. The processor fan may fail for several reasons:

Dust is preventing the fan from spinning smoothly.
The fan motor has failed.
The fan bearings are loose and “jiggling”.

Often you can tell if there is a fan problem by listening and/or touching the computer. A fan that has loose bearings starts jiggling and vibrates the case, making a characteristic noise. You may barely notice the noise at first, and it’s common for even the experienced computer pro to overlook this change. But as time goes by, the sounds and vibrations will become so prominent that you’ll change the fan out just to stop the racket!

You don’t always need to replace the fan. If it is covered with dust, you can often spray away the dust with compressed air. Note that even though you might get the fan running again, its life span has likely been reduced because of the overwork. You should keep an extra fan in reserve in case of failure.

There are a number of utilities that will track the temperature of your processor and case.

2. Bad RAM — Several situations can lead to a bad RAM relationship with a particular machine:

RAM timing is slower than optimal machine spec.
RAM has minor flaws that only appear on detailed testing.
RAM is overheating.

In the “old days” of Fast Page RAM, buying new RAM for your computer was a pretty simple affair. You just needed to know what speed your motherboard supported and the maximum each slot would take. Today, there are many different speeds of RAM, and the better motherboards may be tolerant of using RAM that does not match the motherboard’s maximum specs. For example, your motherboard may support PC133 RAM but will still work with PC100 RAM. But be aware that you may see performance decreases if you install RAM that is slower than the maximum spec.

Minor flaws in RAM chips can lead to system slowdowns and instability. The least expensive chips often have minor flaws that will cause your system to slow down or Blue Screen intermittently. Although built-in mechanisms may allow the system to keep working, there is a performance hit when it has to deal with flawed RAM chips.

In the past, no one worried about RAM chips getting hot, because they didn’t seem to generate much heat. But that’s changed with newer RAM types, especially SDRAM. To check for overheating, open your computer’s case, power down, and pull the plug out. Ground yourself and touch the plastic on one of your RAM chips. Ouch! They get pretty hot. If you find that your RAM chips are overheating, you should consider buying a separate fan to cool your memory. If your motherboard doesn’t support a RAM fan, you might be able to get enough additional cooling by installing a fan card that plugs in to a PCI slot.

Tip: Some motherboards will even allow you to mix speeds but will default to the slowest RAM installed.

3. Failing hard disk — There are many signs of imminent failure before a hard disk finally gives up. Some of these signs include:

Slow access times on the affected drive.
An increasing number of bad sectors when running scandisk and chkdsk.
Unexplained Blue Screens.
Intermittent boot failures.

Detecting a failing hard disk can be tricky because the early signs are subtle. Experienced computer professionals can often hear a change in the normal disk spin. After the disk deteriorates further, you’ll see the system crawl to a standstill. Write processes will take a long time as the system tries to find good blocks to write to. (This will occur if you’re using a robust file system such as NTFS; other file systems will likely Blue Screen the computer.)

When you notice the system slow down, run scandisk or chkdsk, depending on your operating system. If you notice a bad sector where a good sector existed earlier, that’s a clue that the disk is going bad. Back up the data on the disk and prepare for it to fail soon. Make sure you have a spare disk ready so you can replace it when it fails, or replace the disk as soon as you notice the early signs of failure.

Disk noise and scandisk/chkdsk are your best indicators for identifying a failing drive that’s leading to a system slowdown. However, if you are managing a system remotely, or you can’t take the system down for a full chkdsk/R, you can use tools that monitor disk health, such as Executive Software’s DiskAlert.

4. BIOS settings — One often-ignored culprit of system slowdown is the machine’s BIOS settings. Most people accept the BIOS settings as they were configured in the factory and leave them as is. However, slowdowns may occur if the BIOS settings do not match the optimal machine configuration. Often you can improve machine performance by researching your motherboard’s optimal BIOS settings — which may not be the same as the factory defaults.

There is no centralised database of optimal BIOS settings, but a simple Web search on your motherboard name and BIOS as keywords should yield the correct settings.