I forget my root password. So I want to login by single-user mode. I added a parameter single in the end of command.
But the machine run and stop in "Building Window Manager".
why?

what is this ''Building Window Manager"
is it any deamons. then try to load the system in interactive mode and chose not to load the deamon

Interactive mode? Hmmmm... That's a RedHat init script capability. Other distros don't have it (Mandrake might have it, though).

When you get to a LILO prompt, type "linux init=/bin/bash". This will give you a root prompt without logging in. The root filesystem will be mounted read-only. You'll have to remount it as read-write, edit /etc/passwd, make your regular user account's UID zero, then run the "sync" command a couple of times, cross your fingers, remount the root filesystem as read-only, and reboot.

Next time just log in with your regular user account, and you'll be giver root privileges by default. When logged in, just run "passwd root" to change the root password. Then edit /etc/passwd and restore your normal UID (make sure it's the same as before).

Well, that's pretty much it... Good luck! Be warned, this is a risky procedure, can get your filesystem messed up! In the future, don't forget your root password!