being that you are running windows xp, you might want to try the nifty 'repair' option built into that os. believe it or not, it actually works sometimes. there are times in xp, where the nic card will start going goofy /tcp/ip stack gets corrupt, etc.

under network connections, right click on your active connection. hit 'repair'. windows xp will reconfigure your card. your settings will be saved. it takes only a moment, and is pretty much hit or miss. i have seen instances where cards will just stop sending packets all together, but continue to receive. most of the time, this simple 'repair' function will set things back to normal. worth a shot at least.