The answer to this question depends on many factors. The computer freezing can be software related or hardware related. The computer engineer with a lot of experience can definitely tell why a computer freezes.
Software related freezes can be caused by a virus, an incompatible driver, or even operating system design errors, but this is very rare.
Another factor could be the hardware causing freezes. This can be from memory faults, hard disk faults, overheating the CPU, etc.
To tell what is wrong with the PC straight away is almost impossible. To find the freezing cause, it is best to use fault isolation. This is a universal method, and used by many engineers in the PC and Mac worlds.
The main principle is to perform a test, isolate a part of the hardware and perform a test again. Then, if the fault still exists isolating another part of the hardware, a test example would be memory called a RAM test.
If the computer freezes completely, and even the cursor does not move, the best way to start is to test the memory. We have seen many cases when such a system freeze was caused by faulty laptop memory. Faulty memory or RAM is very rare, but it happens from time to time. Sometimes, the memory fault is hard to diagnose. For example, if the faulty cell is at 1.7 GB and the computer uses up to 1.5 GB everyday, then this fault will be completely masked for a long time.
Figure 1: Faulty cells in a computer memory module.
To test the memory, the best software available out there is Memtest. It is a bootable CD. It needs simply to be downloaded to the working system, burned to a CD and then booted on the freezing system.
If this test shows a message in red, congratulations, you just found the cause of your computer freeze.
If the computer is slow and freezes sometimes, but the cursor still can be moved, there is a very high probability that the hard drive is faulty. In other words, the information from the hard drive read is different than when it was written.
This is especially frequent for hard drives that are over three years old. There is special software to test the hard drive called HDTune. It is better to take the hard drive out, connect it to another computer and test it.
If the bad sector shows up as shown in the image below, the freezing causing the fault has been found.
Figure 2: A bad sector on the disk can cause computer freezing.
If the RAM and the hard drive are okay, then this problem is probably caused by its operating system. And, the laptop needs to be checked for overheating. Usually, overheating is caused by the dust that clogs the heat sink. The overheating issue is well known on modern MAC and PC laptops.
If the freezing still happens after the reinstallation process, then probably the CPU or the motherboard are faulty.
There is also possibility that the computer has a faulty motherboard. The components that the computer repair engineer can replace would be capacitors, inductors and probably MOSFETS. Sometimes, the cost of the elements is very high, and probably the best way to fix it is simply to replace the motherboard, or buy another computer.
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