Missing a RUN statement is normally not that big a deal. If you are running the code interactively and forget the RUN (or QUIT for the procs that need that instead) on the LAST procedure or data step then just that step won't until you finish defining it.
Most likely if it seems to not run any code you submit then you have given it unbalanced quotes (or possibly other things like parentheses or macro definitions) and it is just waiting for you to close them.
You can sometimes recover from that state, but restarting is usually the surest way to get back to a stable state.
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