It would help if you had provided a little more information.
When you say “after installed the second dns” do you mean “after the second DNS server was installed on our network” OR do you mean “after the windows xp pro station was configured for a second DNS server” ?
You also need to tell us what kind of DNS servers they are.
Traditional Unix/Linux (BIND), Standalone Microsoft DNS, Integrated with Active Directory? Are they also PDC’s or BDC’s, etc.
I would guess you’re probably talking Active Directory – since the XP user can’t log in – but there are many other variables. Is there a possibility that you have two A/D controllers for the same domain which don’t talk to each other?
Without that information, I wouldn’t even try to speculate on where the problem might lie.