Issues on Installing Windows XP Service Pack 3 on Compaq Presario SR1000

I have a computer named Compaq Presario sr1000 and it is 7 years old. I have installed windows XP on it. The problem is that I want to install XP service pack3 but when I am trying to install this version of windows that problem are occurring some time any of the files of windows will be missed or sometime the files of the Windows XP service pack 3 was corrupted. Then I have to restore the computer to its first point where the computer started. Can anyone understand this critical situation of my computer then please send me the solution.
