This is bit tricky and I'm not saying that Norton caused it.
This has occurred on a few occasions; once, earlier in the year, another time within this month and just now.
When I started up my computer it would stick on the load screen with the hard drive activity light constantly blinking.
Each time I was able to boot into Safe Mode
I ended up Ghosting back to a previous image, which was fine, as I decide to update them and what not, after I transferred whatever files I needed to my second partition.
This time I decided to tackle the problem.
I tried using the Windows Repair Disc to fix any startup errors but I stopped it after 10mins as it wasn't getting anywhere.
I started up in normal mode again to see if anything was done not expecting anything. I entered my password and was distracted on my phone. I'm guessing a few mins must have passed and I saw invalid password. I noticed the hard drive light had stopped blinking constantly and I figured that it just might load now. I entered my password correctly and it did.
Now, after Windows loaded up everything. I saw Norton notifying me that each of its components had been disabled but the Norton icon was green :-S I tried opening it but nothing happened. I checked the Task Manager and I saw that all 4-related processes were running (2 for NIS and 2 for NM).
I decided to see what I could find out online. I opened IE9 - no internet, although Windows says that I am connected. I tried the other browsers - same thing. I tried pinging my router but I was unable to (can't remember the reason but I think it was General hardware failure).
My net and router was working since I was able to use it from my phone.
After this I decided to uninstall NIS completely, restarted and it booted as normal.
I haven't re-installed it yet but I do think it would startup normally.
I'm just putting this out there and will update this after I re-install.
NIS2012 (latest version) | Windows 7x64 | No other security software
Mitka