Windows XP -'Blue screen' after Ctrl-Alt-Delete

I am a desktop technician for my company. We use Windows XP Pro with Novell client on PCs in a mixed NT 4.0 and Novell environment with DHCP. Recently, the NT 4.0 domain was upgraded to Active Directory - Server 2003.
Since then , random computers have been hanging right after Ctrl-Alt-Del is pressed to log in. If I power off the PC and wait a few minutes and try again, it usually fixes itself. It does not do 'Blue Screen of Death',the login box just disappears and you only see the blue background.This is becoming a too common of occurrence to ignore.
I have tried to add/remove the PC from the domain. Someone suggested disabling the WebClient service, which I tried, and flushing DNS, which I tried. They do not seem to be fixing the issue permanently.

Please Advise

 

if you're logging into the AD first, try changing your provider order on the client. Move the Microsoft Windows Network client to the top.