I have to share this because I'm sure someone else will run into this eventually.
I installed the Windows 8 Preview and really liked it right away. Got everything up and running. Setup the 'Live' portion using my Windows Live account credentials. Win 8 uses this 'Live' login instead of a local login once you have it setup presumably so that all the online services start up with the OS.
So, my first reboot the new log in screen comes up and it won't take my password. I get the error 'user name or password incorrect.' I re-installed the OS three times carefully mapping my progress, the final time I rebooted immediately after finishing the initial install - same problem.
Turns out the Live login component in Windows 8 does NOT accept passwords longer than 16 characters. My password is 20 characters.
Two solutions, change your password to Live to 16 or less BEFORE setting up the Live log in component to Win 8 OR input just the first 16 characters of your 20 character password. (Inputting 20 will return the error.)
I hope this helps. This was one bear of an issue for me but it is behind me now...
License to kill gophers.