I have a eos40D, when

Hi. Good Camera... Not being funny.. But do you have the instruction manual. If not first try resetting the camera. Once done, if you can live without live view don`t bother setting it up.
How to reset:-
-set the mode to manual
-press menu, scroll to the third yellow box with the spanner icon.
-scroll to Clear all camera settings,choose clear and confirm your choice.
When you are shooting make sure your lens is switched in AF mode.
Try this first and get back to me.