ie6,ie7下a标签无法点击

li{
    width:149px;
    height:192px;
    position:relative;
    float:left;
    margin-right:7px;
}
.hover_box{
    display:none;
    position:absolute;
    z-index:2;
    width:149px;
    height:192px;
    top:0;
    left:0;
    filter:progid:DXImageTransform.Microsoft.gradient(enabled='true',startColorstr='#99000000', endColorstr='#99000000');
    background:rgba(0,0,0,0.6);
    color:#FFF;
    /*background-image:url(about:blank);*/
}
.hover .hover_box{display:block;}
.pic{display:block;position:relative;z-index:1;}
.pic img{display:block;}