Start up in Safe Mode
, go to Apple menu > System Preferences > Accounts > "your account" > Login Items, remove all login items and reboot. Make a note of each login items and add them one at a time rebooting each time until you get another blue screen startup. Reboot into Safe Mode and remove the login item that caused the blue screen. Keep testing the login items until there are no more that causes the blue screen startup.
If that doesn't work try something from here.