I have a Kobelco sk210. It has no hydraulics at all when we parked it a few months ago it worked fine.
First check the safety lever and the operation of the circuit on your left console that will deactivate the hydraulics of your machine. Make sure it works mechanically and electrically to send the pilot pressure open signal from your hydraulic system. If all of this is okay, be sure to check all fuses and relays, as well as the wiring and connector pins for any corrosion or damage. Also look for any kind of rodent or pest damage. Check the inside of your hydraulic filter and oil for fine metal or shiny-like debris on the oil and filter, indicating a possible component or pump failure. It is also recommended that you check your pressures and confirm that they are within the factory specifications for your model and the serial number of the machine.