Goes To Standby

i have this monior connected to my mack, the cable works fine, howeather the monitor works perfectly for about half an hour, but after that, the monitor goes to standby and the logo apperears on the monitor, but when to logo comes up, the monitor still stays connected but you cant see the display. once this has happend once, it keeps rehappening ever 10 seconds or so, and when the logo has gone and the monitor goes back to normal again, there seems to be a slight flickering of the display it this a overheating problem? or something else once i finish, i switch off the monitor, and then when i go back to using it, it seems to work for half an hour again and then repeats the process thanks.