All installed plug-in not found in dashboard but still in plugins folder

Hi, Really need help. All my previously installed plug-ins including event managers and mailing list etc were lost (ie not shown in dashboard) after installing an “advance social sharer”. However I can still found those plugin under the /plugins folders and files in there seemed intact. I suspect some kind of index file were corrupted during the new-plugin installation. Could someone kind enough to show me how WP looks through its plug-in list please? Many thanks!