Plot3D command yields -Graphics3D- [closed]

When I use a Plot3D command, the response is -Graphics3D- and no plot. What am I missing ?

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You're missing a front end. –  rm -rf Jan 9 at 19:50
Are you running the command line version of Mathematica (started with math on Linux)? If so, this is normal. If not, restart Mathematica. If after the restart you still see the problem, please tell us if you modified any settings (and which ones). –  Szabolcs Jan 9 at 19:54
To use plots in the terminal: mathematica.stackexchange.com/a/13963/5 –  rm -rf Jan 9 at 19:54
Perhaps pre-6 version of Mathematica with a redirected DisplayFunction -> ... in Plot3D and a missing semicolon from the end? Could you please specify the version and paltform you are using, and the command that produces -Graphics3D-? –  István Zachar Jan 9 at 20:06
Closing due to lack of feedback. I'll consider reopening once you, say, reply to any of the other comments. –  Ｊ. Ｍ. Apr 28 at 15:13