whereabouts are you? Could be a duff pump - works ok without pressure, but unable to push against back pressure when brewing. can't quite see from the pics. Is the broken screw the one in the centre of the brew head? There are ways to remove screws, but you will need to have clear access so you can get to it. drilling the centre of the screw and using a hex key tapped info the drill hole sometimes works - also, as am says do it hot. I wouldn't waste time on the screw unless you know that everything else is fixed, because machine may not be worth fixing.
