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: [http://support.apple.com/kb/HT2674|Intel-based Mac: Startup sequence and error codes, symbols].
Here's a good write up on diagnosing a Blue screen condition: [http://macs.about.com/od/MacTroubleshootingTips/qt/Troubleshooting-Mac-Startup-Problems-Stuck-At-The-Blue-Screen.htm|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.