Had this issue this morning.
Got on the server in the environment and found that there were some log messages about an event id 504 folder redirect error.
Rebooted the file server that hosted the user home directories.
Nogo - still hanging at the welcome screen.
Got a remote session with an older XP machine and found that the connection was painful, even though the connection via the firewall to the server was snappy...
Hmmmm, probably a nic running it's mouth off eh?
Down all machines but the workstation with the remote and found the ping times to the server went from 3-4 seconds to < 1ms!
Bring them back up 1 at a time until the suspect is known!
Long story short, sometimes a "server" issue is not a "server" issue, but rather a workstation issue!