[Lynne]

Except the only examples I see right now are for forums with new posts and you only added the css for regular sub-forums with old posts (as I said, use firebug to get this stuff).

and you certainly don't want the stuff regarding the position unless you are using a sprite (which is why they would 'disappear' when you used the CSS for the old posts forums) and your image is not 10x11, it's 14x14, so you need to put those dimensions in.

.forum-list-container .subforum-list .subforum-item .icon.new, .forum-list-container .forum-item.sub.new .cell-forum .icon {
    background: url("http://www.premierleagueforum.co.uk/images/crests/ars14x14.png") rgba(0, 0, 0, 0);
    display: inline-block;
    height: 14px;
    width: 14px;
}

and, this image seems to be missing from your site (for your Support & Feedback forum):
images/icons/suppico.png