Not a lot of information to go on in your post. The white screen after booting sounds like X and/or the desktop login manager is not starting up correctly. If you hit CTRL+ALT+F1 do you get a text login prompt? If so login as root and type "init 3" (no quotes_ to stop the graphical environment (this command brings the system down to runlevel 3 which does not start the graphical login manager). Then logout as root login as your regular user (you did create an unprivileged user account, right?). Then type "startx" (again, no quotes) and see if the desktop starts up normally.
If the boot is hanging in other places, please give us the last message printed on the screen before the hang.