no playback sound

Just bought Cubase LE5 with Lexicon IO22. Can’t hear playback through speakers connected to the IO22.
The ASIO driver is configured to IO22 in Cubase Device Setup/VST Audio System.
I can record through “add track” and instrument. It shows on the grid.
However, no playback is possible.
Youtube for example CAN be heard through the sound card. Why not cubase?
Please HELP ME