st4s not starting

ST4S was running fine. Unplugged battery and black box while working on bike. refitted and bike does not start. As in key in, neutral light on, clutch held in, sidestand up. The ecu light goes out the fuel pump ramps up but nothing happens when you hit the button. Initialy when I turned it on the fan ran for a while as well, but now it does not do that, although that might be a red herring having had the radiator , refitted and filled up. Your thoughts welcome.