Since patch 4.0 I have had difficulty logging in. The first attempt results in 2-3 of the 5 accounts successfully connecting. The other accounts will just hang at the loading screen for several minutes until getting disconnected. Apparently many people are having this problem. Here is a way to log in without using ALT-F4 to kill the windows that won't connect.

1. (on xp) Go to Start-> Run> 'COMMAND'

2. type IPCONFIG /RELEASE but don't press enter yet

3. use isboxer to start your WoW accounts

4. attempt to log in

5. if any of them hang, alt-tab to the DOS window and press enter. this will disconnect the accounts, even the hung ones

6. type IPCONFIG /RENEW and press enter

7. alt-tab back to WoW and log in again. you can do all 5 or however many simultaneously. they will all connect and log in this time.