I'm not at my computer atm, so can't try the disabling of plugins yet, but thought I'd get an answer out there for this stuff.
I haven't updated any plugins today (or within the last week or two), but I'll certainly try disabling and see if the problem is there. It shouldn't be antivirus as that hasn't changed either, but I can disable Norton for a brief time and verify.
@BetterRed - Yes, I can do other things while calibre is loading, although usually that consists of browsing via Firefox. It's sluggish and at times needs more than a few seconds to process what is usually instantaneous, but my system isn't locking completely up.
I was hoping for a debug command that logged what is actually happening in the background - so it would show that x time was used for x part of loading the program. Would be easier to troubleshoot if there was one, even if I only understood a fraction of what it said.