You could disconnect from the Internet and stop and start the FW service and see if the clears your problem.
There is a command that you can enter at the Run Box to access XP FW settings. I don't remember what that command is you'll have to look it up using Google.
Now, I am not saying 100% that malware has taken it out, but something like that is just not going to happen for no reason. You might want to search Google for malware that will disable the XP FW or parts of it and how to remove it.
If push comes to shove, you can do an upgrade/install over the top of the existing XP O/S that will not destroy anything but lay the O/S back down leaving everything intact to see if that corrects the problem. You'll have to apply any SP and all updates again if you do it.
If the machine has a direct connection to the modem, then you should try to secure the XP O/S harden it to attack as much as possible. If the O/S is not secure, then nothing running with the O/S is secure.
I am glad you got a fix for your problem. But after seeing this, I for one now question the abilities of the XP FW, particularly if you have been running for awhile and this started happening out of nowhere.
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