Once you get to the boot: prompt, type
root=/dev/hda1
If your root partition is different than /dev/hda1 please put in the correct one. This should get you to a command line. You can then do
less /var/log/messages
at the prompt and it will display that file that JStew mentioned. Use your up and down arrows to scroll through the file. Hopefully you'll find some error messages explaining what is going on. Let us know if you run into any problems. Hope this helps.