If the camera was working before you changed the batteries
the problem has to be either the batteries are installed wrong or one (or more) of the batteries is bad.

Get out your the Basic Camera User Manual and look on page 1.
There is a picture of how the batteries should be installed.

If they are correctly installed then one (or more) of the batteries is bad.

Look at the batteries and see if they are alkaline batteries or NiMH batteries.
If they are alkaline batteries, go and buy 4 new batteries.
If they are NiMH batteries they need to be charged before you can use them.