This happened to me today in SW21 SP2.

Suddenly, the part appears, but no features and I can't save or any of that kind of thing. 

The "viewing" notation in the upper banner makes me think the system thinks it's still loading, but previously (yesterday) it opened just fine. What might I have done, and what can I do to fix it? This file is no use to me as it is. 

The part is shoved over to one side on purpose.