This is a known problem in version which has been fixed with the free update to version The crash is caused because the Show Folder List setting was turned off under the View menu. If Show Folder List is left checked, PowerDesk will not crash.

To open PowerDesk again, Run PDEXPLO.EXE with the /e+ command line parameter.

From the Start Menu > Run line 
Type C:\Progra~1\Ontrack\PowerDesk\pdexplo.exe /e+
Press enter
Then run EasyUpdate from the PowerDesk help menu
Alternately you can download the update to version by running EasyUpdate from the Program Start Menu. Start Menu -> Programs -> PowerDesk Pro 5.0 -> Easy Update.