Two appearances of a blue screen indicates user level issues. You should only pass to the blue screen when the system is fully booted and ready to hand off to the user start part of the process.
You can troubleshoot this with three small changes:
- Disable automatic user log in to separate the user from the system.
- Open Startup Disk system preference and ensure the correct drive is selected to boot.
- Power down the Mac and then boot in safe mode once to rebuild a few databases that could be causing the corruption or slow boot process.
Once you start into safe mode, log in or not, but shut the Mac down cleanly and then re-test the startup sequence. Should the symptoms change or nothing change - you will have isolated the issue and eliminated three likely potential causes to a slow reboot that eventually works, but is troublesome from a speed consideration.
Also - you might start with step 0 - make a good full backup of the system before investigating further since if the hard drive is beginning to fail - you'd rather have a good backup before you try fixing things in case the time left to run before failure is small.