HAL uses the hald daemon and also depends on the dbusd daemon. If either of those have a problem, you could have a problem but usually it amounts to automounting of external drives not working. One quick thing to check is if you use the acpi=no kernel boot option. This option probably isn't needed and will prevent dbusd from starting.
One kernel boot option I have needed is the "nolapic" option.
Other than that, I think you need to read the boot log. You may need to boot up with a live distro version to access your systems log files, if it can't boot. If this is a new installation, and you used gparted to partition your drives, look under either /etc/hal/fdi/policy/ or /usr/share/hal/fdi/policy/ for a file with the string "gparted" in the filename. I've read that gparted has a bug where a temporary policy file is created prevent dbus from starting back up and then dbus is stopped. The bug is that this file isn't deleted when you are finished.
You mentioned that you are locked out, so from this I'm not certain if the computer finishes booting or not. Does Ubuntu use policy kit. The PolicyKit package is involved in dbusd and hald permissions and also supplies a PAM file which could be your access problem. I haven't studied it so you may need to resort to other replies or use a Google search.