Since you haven't bothered to actually mention what sort of
problem you're experiencing, I'm going to take a wild guess.
If you connected the PC to the Internet without having first
installed the KB824146 Hotfix, without having first installed an
antivirus application with current virus definition files, and before
enabling a firewall, you're very likely to get infected from any of
the thousands of PCs on the Internet that are constantly broadcasting
the worms.