Some of you may face or might have faced the problem widely known as the blue screen of death.
If your computer starts normally and show windows xp loading but doesnt boot displaying the blue screen then you have a serious problem. If this kind of problem happens then try to re-install windows xp. If the computer gets jammed while installing windows xp and shows the blue screen again then be sure that you have a problem in your power supply.
I have gone through this problem and replacing the power supply fixed my PC.
Hope this will be helpful for someone. If you have knowledge about hardware or computer troubleshooting/fixing then please feel free to share anything because i want to gain knowledge.