Space is a long, long, long way away – so sometimes there is no video available and sometimes the ISS is on the “Dark Side”!
If there is no Live picture here it can mean a number of things –
Firstly the Earth might have disappeared or maybe the explanation could be something simpler.

If there is a Black Image this could mean that International Space Station (ISS) is on the night side of the Earth.
If there is a Grey Image this could mean that we are momentarily switching between cameras, or that communications with the ISS is not available.
There is no audio. No one can hear you scream, so please add your own soundtrack.

For a display of the real time ISS location plus the HDEV imagery, visit here: http://eol.jsc.nasa.gov/HDEV/
To learn more about the HDEV experiment, visit here: http://www.nasa.gov/mission_pages/station/research/experiments/917.html