Why computer freezes

The answer to this question depends on many factors. The computer freezing cause can be software relate or hardware related.
Software related freezes can be caused by a virus, a incompatible drivers, or even operating system design errors but this is very rare.
Other part is a hardware caused freezes. This can be from memory faults, hard disk faults to overheating the CPU etc.
To say what is wrong with the PC straight away is almost impossible. To find the freezing cause best way is to use fault isolation. This is universal method and used by many engineers in PC and Mac worlds.
The main principle is to perform a test or isolate a part of hardware and perform a test. Then if the fault still ezsist we perform second test or isolating the hardware. As test example would be memory so called RAM test. As example we can take the DVD drive from the laptop and then see how it works. We had once a freezing laptop which was with a faulty DVD drive. After the replacement everything worked perfectly.

If the computer freezes completely and even the cursor does not move the best way to start is to test the memory. We seen some of cases when such a total system freeze was caused by faulty laptop memory. Faulty memory or RAM is very rare but it happens from time to time and we cant overlook it.
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 then burned to the CD and then booted on the freezing system.
If this test will show some message in red then congratulations you just found the cause of computer freeze.

If the computer is slow and freezes sometimes but the cursor still  can be moved then very high probability that the hard drive is faulty. In other words the information from the hard drive is read is different than it was written.
Especially this is frequent for hard drives that are over three years old. There is a special software to test the hard drive HDTune. Better is to take the hard drive out connect it to the another computer and test it.
If the bad sector will show up as shown in the image below the freezing causing fault has been found.

IMAGE

If the RAM and the hard drive are ok then this probably is caused by operating system. Also if this is a laptop needs to be checked for overheating. Usually overheating is caused by the dust that clogs the heat sink.

If the freezing still happens after the re-installation then probably the CPU or the motherboard are faulty.

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