Try 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.
Try it from the guest user. They show there?
If they do, try removing com.apple.finder.plist and com.apple.sidebar.plist from ~/Library/Preferences. You can get there (with Finder active) by holding Option, clicking Go at the top of your screen, then Library. Then reboot.
Boot up holding command-r keys into your Recovery Volume.
The screen should give you these choices...
Restore from TM backup
Reinstall Mac OS X
Get help online
First run Disk Utility Repair Disk, if you get errors run until no errors reported or reports "the disk cannot be fixed". Then, choose Reinstall OS X. This will be an install "in place" and shouldn't effect any of your own data or settings. That said, you should always have a backup.