Program Upload Loading problem
It can have many options, the main reason is it cannot communicate with the Nano.

I try to create a list with options:


Hardware issues


Nano is broken (solution: change Nano)
USB cable is broken (solution: change cable)
USB port is broken (solution: change USB port)

Software issues


USB port 'corrupt' (solution: use another USB port)
USB connection incorrect (solution: reconnect USB cable)
IDE is corrupt (solution: reinstall IDE)
Nano in illegal state (solution: reset/reconnect power of Nano)
Serial communication is used (remove RX/TX wires)