l found the problem n the solution for my case, im 100 percent sure that its the nexus 7's micro USB port that causes our problem it is probably loose n dirty (it looks pretty clean but its rubbish believe me) either you ve to get micro USB port replacement or get it clean n tight, i used electric isolating bandages( very tiny bit) around the slimport usb out so that when i entered it into nexus 7 it fit tight into port n that was it ! No more 'no signals' any more, u can use it with or without the charging cable it makes no difference, also pls dont boder changing ur HDMI cables with expensive or short ones, remember its the problem of your device's micro USB port causes that signal losses
Good Luck Folks God Bless