Some WHDLoad programs may result in a black screen being displayed. This is sometimes caused by the program not being configured in the WHDLoad package, or if the program file has been renamed.
Also, THEA500 Mini will prepare the contents of the USB stick when you first launch a program stored on it. While doing this the Drive LED will flash regularly, indicating that you should not remove the stick or power off THEA500 Mini.
The latest verson of the WHDLoad Package (v1.0.1) reduces the occurance of black-screens as well as adding a number of new programs.
See Why do I see THEA500 Logo for further information.