Nautilus Restart Locked up my Computer

[jimkvg at 3web.com]

I installed Dropbox and then it required Nautilus "to be restarted to function properly."  When I clicked on "Nautilus Restart", my computer went locked up.  Keyboard won't work and mouse arrow won't move around.  I resorted to pushing the power button to shut the computer down.   It happened in the previous version of Ubuntu 14.10 and then again in 15.04.  Is there a way to fix this problem?  Your tips or help'll be greatly appreciated.  Thank you.  

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