Have you tried starting in Safe Mode and see if the problem still occurs?
Restart holding the "shift" key.
(Expect it to take longer to start this way because it runs a directory check first.)
If this works look in System Preferences > Users & Groups > Login items and delete any third party login items (-), you can always add them back with the (+). Also look in /Library/Startup Items. Nothing is put in that folder by default, so anything in there is yours.