I had trouble with my steamwand, so opened the machine and changed the rubber gasket.
Now steam is perfect again, but suddenly there is no light in the espressobutton, so I cannot turn it on.

I am wandering what could have happened - all seems to be connected still

Open it back up and check the wire connected to the button. Trace the line and make sure the connectors are fully seated. Could be a coincidence that the light goes bad at the same time you opened it up, but it seems more likely that it was something incidental.

Did check all lines - cannot see any fault anywhere - but no activation when trying to brew. But perfect steam and hot water.

Still not working.

Steam is on, but the pump does not turn on - I just emptied the hot water/steam... and pump does not start to pull in water again.