try reseting the PMU... and if that doesn't work try replacing the pram battery, if that doesn't work boot your computer in target disk mode and get your files off onto another computer, and off to the repair shop for you..
Digital Light Graphics And Animation
there are other technical solutions (fsck being the primary one), however when you can't boot, you would typically boot to the command line and run a few utilities, but if you're not comfortable doing that, then diskwarrior is a valid option in most cases...
I'm not sure what I'm going to do. I am at the tail end of a project that I would love to get out the door before I rebuild the computer. I guess I'll check out the apple tools to see how easy it would be and then decide.
Should I still reset the PMU and replace the pram battery?