SES Code Reads P0440, Evap. Emission System

I do not know anything about the Evaporative Emission System, so any help would be appreciated.

The SES light would come on only every few times I would start the car, (01 GT) now it is on constantly. Got it scanned and I got a list of possible problems;
1 loose gas cap (almost positive its not this)
2 Evap canister hose not connected
3 Vent solenoid defective
4 Vacuum leak at engine
Where/what would i look for to diagnose the problem and find out what needs fixed?

Thanks

do you get the check gas cap light on??? if you do then you might just have a defective gas cap, and that could solve your problems...let me know....