It is very important to check a used computer thoroughly before buying, because it can lead to problems in the future. A hard disk show no outward signs but may be deteriorating. In the same way that the needle may slip suddenly and may cause scratches on the disc ultimately leading to loss of memory as computers can fail at any time. If proven, the faults that may occur can be known. Consider first the possible failures that may occur while buying a used computer.

Hard drive failure can happen due to heavy wear over a period of time. The read-write heads of a hard disk are used to recover or re-encode the data stored on the hard drive with the help of a disk platter that spins at high speed. Over a period of time the risk of failure or malfunction of the disc increases. Bad sectors hard drives can be found only if a full surface scan is done on the computer used. The scanning time depends on the capacity and size of the hard drive of your computer. Many skip this procedure because of the slow process of scanning the entire disk and end up buying a used computer with a bad sector.

Monitors should be checked for faults. The malfunction of a monitor is called a "dry joint" which translates into the monitor does not work after being heated. This can be checked if the monitor is made to work for a minimum of 20 to 30 minutes after turning on the computer.

Next is to find all the possibilities of the central processing unit to get frozen. Normally, all central processing units have a heat sink and fan to keep the unit cool. Over a period of time fans can not function properly due to the accumulation of dust and dirt resulting in overheating of the central processing unit and even to stop working. When buying a used computer the fan needs to be checked and if any abnormal sound is heard, not good for the purchase.

The equipment used can have a greater chance of getting crashed and froze due to the use of the operating system for a number of years. There may be a cache or RAM failure due to the exposure that leads to data loss. To increase the performance of the computer and to avoid crashing, the computer operating system used can be reinstalled with a new operating system or a new one.

During the audit of the computers used by the failures, it is good to disconnect the network connection if present before testing. It is also advisable to check the units, such as CD or DVD by opening and closing them and also to touch something in the units to see how they work. The computer monitors can be checked for resolution and brightness of color trying different options, settings, etc.. To check the hard disk size the CMOS setup can be gone through and to check the processor speed, cache and RAM you press the pause button when it appears on the screen during the boot process. To check the boot process, the computer can turn on and off a couple of times and seen how he responds. Testing should be done to see if all passwords are erased before buying a used computer.

The first product on your servicing guidelines should be a evaluation of all the applications that are packed onto the pc. You may see device cafes, press gamers you don't use or an obsolete system.

To me what I normally  do if I purchase used computer is to format it and install new programs relevant to my need . With this you know that there shouldn't be any security hole in your computer.