My Import window isn't working properly

Possibly a numpty question, since I'm very new to FCPX, but...

I've updated to FCPX 10.0.6 and Importing media fails. I do File -> Import... or Cmd-I or click the Import Media button, and all that happens is that the FCPX window dims. There's no other dialog or prompt, and I can't get back to the main window although the menus are active (but with most options greyed out). I can't work out how to back out of this, since nearly every key or combination I press just gets me the default system 'oops, you can't do that' beep. I have to Quit FCPX, and then I get a crash report.

Where have I goofed?

Cheers,

James