Which product is this?
Have you tried the sqlplus client?
You didn't explicitly say, so I have to ask - did you try restarting SQL Developer? Sometimes the JVM goes 'fuzzy' and I see behavior like this, and a restart fixes it 95% of the time.
I was running queries, having a good old time. Im now without a query result window. Every time I run a query (ctrl + Enter, f9, or Larger Green arrow click) I get no result window. I have looked thru all menu items, known issues list in readme, and I have done the Window>Reset Windows to Factory Settings option. no luck. If I hit the "Run Script" button, (f5) I get the output in a text format, but that is junk. Any ideas? im frustrated with product completely right now, and fully prepared for someone to tell me the stupid fix so i can feel stupid, and feel better at the same time !!
I can reproduce your 'problem' - you 'accidentally' clicked that little black 'down' arrow that collapses the result window.
So just click the 'up' arrow to expand it.,
On the left side of the worksheet at the bottom you should see two little black arrowheads - one pointing up and one pointing down.