On the Dashboard, please click on the Cases button in the group of color buttons. This will generate an excel file. One of the columns in the file indicates whether the case is archived or open.
Alternatively, click on the Cases (Projects) tab, then enter % in the search box after unchecking the checkbox next to the search box (or simply clicking on "xxx archived" link. All cases will be displayed in the left sidebar below the search box. Archived cases are shown in a different color.
If you remember a few letters of the case name, entering in the search box will bring up the case. On the right side, click on the Edit Case tab and use the checkbox there to re-open the case, is so desired.