Whenever I try to download any thing it starts downloading. But when it reaches 99% it staps and then nothing does happen. Please tell me whether there is problem with windows or any thing else. I'm using xp2007 sp2

First... make sure you have enough free space on your hard drive.

Which browser do you use? It happened in this way for me in chrome, I'm using FF now. If chrome is the problem for you too, try FF and it works like a charm.