You need more info to try and find out what is going on.
* Hit Ctrl-Alt-F1 when the loading bar is moving to see the messages console. (or Ctrl-Alt-F2 .. Ctrl-Alt-Fx depending on linux system) Ctrl-Alt-F1 should be messages/console and Ctrl-Alt-F7 X/graphics
* At Ctrl-Alt-F1 after it is sitting there doing nothing then do you get a login prompt? Login there and use the command-line.
* Or if you can't login then boot with a System Rescue CD or anything else and mount your disks and check /var/log/messages (same as what you would see hitting Ctrl-Alt-F1) and check other logfiles e.g. can X(graphics start?) check /var/log/X* Xorg.0.log maybe http://lmgtfy.com/?q=system+rescue+CD
* And what were you doing the last time you got a successful graphics session? Were there any changes to X config made? Any packages upgraded or installed? It sounds like you can boot okay but maybe X is in trouble. Check were there recent changes to X config: /etc/X11/xorg.conf