Dashboard warning lights

[my mucker]

Hi all ,the problem i have is, the past 6 weeks or so when I've gone out to the car ,turning the ignition on, and the stop light has been lighting up and also the radiator light has come on,so i am thinking that the rad is low on coolant ??? but when i go and check the level ,it's just below the max line !! has anyone have any knowledge as to what's going on?? ps when i drive around the block ,all warning lights go out !!TIA Gwyn