Do you have an external bootable HD which you can boot your system up? Give that a try.
Here's the Apple TN on the boot up process: Intel-based Mac: Startup sequence and error codes, symbols.
Here's a good write up on diagnosing a Blue screen condition: Troubleshooting Mac Startup Problems - Stuck at the Blue Screen. Sadly Apple doesn't have a good TN on how to fix a Blue Screen from booting only when your in an app.
Most of the time I try using disk Utility a try from a different startup disk. I also try fixing the permissions as well. If I can get the disk to boot up I restart running in Safe mode (or a 3rd party tool like Drive Genius) so the directory bTree is rebuilt.
Often I discover the drive is on its last legs so I end up swapping out the drive.