BuddyPress.org

well,follow these steps

1.Get a backup of bp-themes(I hope you already did it) and delete it from wp-content,there should be no folder named bp-themes

2.Now copy the bp-sn-parent and bp-default from the buddypress/bp-themes(the new buddypress plugin you have downloaded) to wp-content/themes

3.Go to wp-dashboard->Site Admin->Themes and enable bp-default

4.Go to appearance and activate bp-default ,hopefully ,you site should return back to normal.