If you have decided to repair your computer at home, here is a brief guide that teaches you how to do it.
First of all, you will need a proper working desktop or laptop computer to burn a few CDs with the necessary tools. The best one in our opinion is UBCD4WIN. It already has an easy graphical user interface based on the Windows XP operating system. This boot CD needs to be built using the Windows XP installation CD. With this CD, it is possible to transfer files from a computer that doesn’t boot to its USB drive. The USB disk or memory stick must be attached before UBCD4WIN starts. If done otherwise, the drive will not work.
UBCD4Win has many useful programs preinstalled on it such as HDtune and the Avira antivirus.
How to build the CD is explained here (http://www.ubcd4win.com/howto.htm). After building it, you should have a .iso file which can be burned with any CD burning software such as Nero. Set the computer to boot from the CD drive. First, the screen  will appear and it will look like this.
 
We have a few options here. The option Launch “The Ultimate Boot CD for Windows" starts the bootable CD.
Another option like "Memtest 86" will be described later. This is also a very valuable tool.
After USBCD starts, we meet with this graphical user interface.

There is nothing very special about how this looks; in fact, at first look we are reminded of the Windows operating system. On the left side, we can find the usual icons such as My Computer (for browsing the hard disk), the Internet browser (it has the capability to browse the Internet when network function is enabled) and HD Tune.
You can use HD Tune to directly perform what’s probably the most neglected PC cleaning operation—a low level hard disk check for all bad sectors on it.
 
This means that the program will write to the disk a small amount of information and then try to read it. If it can't read, it means the hard disk has a bad sector. In our opinion, even if the hard disk has only one bad sector, it is better to discard it as bad sectors tend to spread over the hard disk after a while. And it's difficult to identify such a fault because the computer or laptop sometimes functions properly but then hangs without any apparent reason. HD Tune has a few tabs as you will see—for the hard disk test for errors, the relevant tab is Error Scan.
 
The entire hard disk test can take about an hour. In the picture, the green area means good sectors and red dots are bad sectors. It shows here that the hard disk has a bad sector. That’s the reason we I have stopped the test because anyway the HDD isn’t any good.

The laptop and computer diagnostic software Memtest is the best software application for testing a computer's memory.
It identifies the processor type and speed, memory type and speed. The testing of 2 GB of memory can take about one hour depending on the system configuration. It uses a variety of data and runs through the memory by writing and reading. If a part of memory can't be read, it means the memory module is bad and not suitable for use. When the test completes, it displays a message like "Pass completed. No errors found". In case bad memory area found it will display a message in red which simply says “ERROR – The memory can't be read” or something similar.