Does the cooling fan come on at all? If not, there's the issue to track down as to why. Could be that the fan motor has given up the ghost, or a solenoid has gone bad, loose or broken wiring, etc. If the fan does come on, you could have a bad thermostat, or the sensor at the radiator that signals the fan to turn on and off could be bad. There also may be an air pocket in the cooling system, which will cause the issue you describe. For the air pocket, you need to locate the bleed screws and bleed the air out. You will also probably have to elevate the front end to assist on removing the air.
That's all I know, which I mostly picked from others on this forum. Hopefully someone else will chime in to add to this.
Good luck!