The problem is likely an issue with your keyboard. If you have a different
keyboard, I'd connect that one and see if you still have the issue. If not,
the problem is the keyboard and not XP.
There seem to be numerous people who have a problem with their Enter/Return
key. This is beginning to look like a software problem NOT a keyboard fault.
If you are one of these people try using the other Enter key on the numeric
key pad. If that also gives you problems then it probably isn't the switch
contacts in your keyboard.
A web search reveals this problem is being reported elsewhere as well.....
"I removed the last secruity update for XP and my enter key started working
again.
Thursday, February 12, 2004 Security Update for Windows XP (KB828028) "
But I don't work for Microsoft so I can't comment recommend this as a
solution.