sudden no stereo output

Opened cubase 6.5 today, and am getting no output . I tried a couple of different projects, I am showing sign waves, on the screen, but not activity on any of the channels or the stereo output. I used it last night and no problem. Any idea what to check? thanks for any help.

i just did an audio mixdown and it works as mp3 but no control on the project?? so the info is there I can’t adjust levels or anything or hear anything in the normal way it should.

found the problem had to turn off the interface and the computer then all is normal. thank.s