I had this exact same problem. No matter what I tried, resetting the machine, or programming, turning off at the outlet switch etc, I was unable to change the volume that poured. The lungo would pour for around 5 or 6 seconds then stop.
I ran a de-scale cycle with de-scaling solution as per the instructions. This instantly improved the flow rate of the machine and I was able to program as normal after finishing the cycle.
Nespresso recommend cleaning every 3 months or 300 capsules so worth trying this before looking for other issues IMHO.