Plugin [Boxer] Boxes Disappeared in IE

PLEASE HELP!! My three boxes appears perfectly in Chrome and in Firefox but NOT IN IE! Only one of my three boxes appeared in IE. I think my IE is IE 7. I know many people still uses this version so please help me to make it look right in IE 7.

I am using the newest version of the Boxer plugin and I use Twenty Eleven Child Theme.

I searched through the earlier posts and I saw that someone had similar problems and they pasted:

.art-postcontent {
width: 750px;
}

in their style.css but i tried to do the same thing at the end of my child theme style.css but it doesn’t make any difference. Please help!

Thank you so much!

PLEASE HELP!

http://www.bwny.org