By shutting down the fuel cells, what will the astronauts not be able to do while they are in space?

The fuel cells are what powers up the spacecraft with regards to its different operations like regulating breathable oxygen and making pot water. The famous incident that the fuel cells got leaked was in the Apollo 13. Their quest to the moon has come to an end when their fuel cells had gone insufficiently to continue the voyage.

2. x2 + 8x + 12 = 0 to prove: x = -6 or x = -2