Yeah, that icon means the system can't find the main boot volume.
This is most likely due to the software being corrupt.
One way this can happen is by force shutting down the computer frequently.
I would get out your mac OS X install discs and run the first one. On the disc is a program titled "Disk Utility." (This assumes you have 10.3 or later).
Use disk utility to "repair disk" on your main hard drive, and then see if it boots.
