PS: I have a power bank with capacity of 5600mAh
Power banks are meant for charging batteries.
Powering an Arduino board from a power bank is problematic, because nearly all power banks on the market have a “power cut-off” (auto-off) feature, while the current drawn from the power-bank falls below a certain limit.
I think, Arduino boards like UNO draw something like 45…55 mA. Mini boards even less.
And the power auto-off of most power banks is at a minumum of 60…100 mA.
So most likely: If your motors do not draw any current and your Arduino board draws less than the auto-off current of your power bank, your Arduino board will see a power loss and shut down due to lack of power after a few seconds.
Even if a power bank has a 5V outlet, you cannot use a power bank for powering low-power devices. They will automatically shut off their 5V output after a few seconds, if you do not draw at least 60…100 mA current to prevent auto-off.