Can you use ports or markets after playing all action disks?
You cannot use the ports or markets if you have no action disks left to play.

The easy way to think about this is:

On your turn:


Place one of your action disks on the board and take that action
(Before or After you place your action disk) 

Use one Evolution card (optional)

(Before or After you place your action disk) 

Pay one coin to use a port or a market (optional)
You can use each market or port you own once per round, and only one per turn.



So if you don't have any action markers, you won't be able to use a port/market.