Z-axis won't move


Yesterday I removed the whole tool head from my Mini and disassembled hot end, heater, thermistor, etc. for cleaning and unclogging the filaments. However, after I reassembled the tool head and put it back on the printer, the Z-axis won’t move at all (it is at the highest or home position). When I clicked the z-axis icon in Cura, I can hear a sound that step motor is trying to turn but it doesn’t really run. The X- and Y-axes are still moving okay. Does anyone know what could be going wrong and how can I fix it? Thanks a lot.

Hey, I found out it was the wire of thermistor contacting the heating block. After I repositioned the thermistor (make sure the wires are covered up by braided sleeve) and reassembled the tool head, the printer works like a charm.