1) go to Banner-->Banners Manager, if you can see correct banner image here at the bottom of this page, image setting is right.
clear every thing in Custom Banner Code, you don't need it.
( use it only you want to use flash banner, it will replace default image show up at the bottom)
wring down the banner client name, you will need Banner Client ID later.
2) go to Banner-->Manage Client-->according Banner Client Name, you can get specific Banner Client ID here.
3) go to Site Module-->Modules Managers--> Your module Name-->Parameter-->Banner Client( ID) , make sure it is correct Banner Client ID.
4) Make sure everything is published.
wish this can solve your problem