The other webcam, focused on units 1 and 2, is up and running, as illustrated in this screenshot from this morning:
There was a 5.6 earthquake reported in north east Japan on Feb 28, 2017:
Eastern Japan shaken by 5.6 magnitude quake, no tsunami warning. Reuters, February 28, 2017, http://www.reuters.com/article/us-japan-quake-idUSKBN1670RM
A 5.6 magnitude earthquake shook a wide swathe of eastern and northeastern Japan on Tuesday, including the capital Tokyo where buildings swayed, but no tsunami warning was issued and there were no immediate reports of damage or injuries.
Japan's Meteorological Agency offers this image of the recent earthquake activity, which appears to be centered very close to the Fukushima Daiichi plant http://www.jma.go.jp/en/quake/20170228165255395-281649.html:
The recent earthquake activity in the region where Fukushima Daiichi is situated raises many questions about the plant's stability.
I hope that the cam trained on Unit 4 is simply unavailable for technical issues that have nothing to do with a disconcerting turn in plant conditions.