I'm not an expert, but I believe this is "limp mode"... when the ECU has detected a problem with the engine so it tries to protect itself by not letting you rev it anymore.
So you can get a diagnostic fault code from the dashboard....
here's a link how to do it:

http://www.youtube.com/watch?v=v2i0e...rleow&index=28

But if it doesn't come up with anything then a garage diagnostic computer should.

Hope this helps.