an Internet Problem

I've been having an Internet problem.
When I start the Internet, Windows XP becomes unsteady, and the hard drive makes a strange noise.
And the most important, I can't update Windows XP. When I tried to update, it continuously downloads something and it never stops, even after I shut down the computer and turned on several hours later.
What's wrong with my PC? I may have virus? But I just finished checking it by through Virus Vaster yesterday (the software is trial version though).
In either there is virus or not, I have to solve this problem as soon as possible.