My windows xp sp3 version 2002 requires activation key but when I installed it i inserted the product key.Now it say 30 days remain...what should I do?

Hi,
Although some product codes which come with computers are good for up to 3 uses, some are only fine for one.

I would Attempt to enter it again (I forget the exact location but a quick google search should say, and of that fails to work I would call Microsoft support and explain your problem,
Hope this helps