I am one of those unfortunate souls without Lomo experience. To cause vignetting take a piece of black material with a hole in it and hold it in front of the lens. The amount of vignetting will be dependent on the diaphram size, the distance focussed upon, the size of the hole in the material and the distance the material is from the lens front. If you make a hole in a piece of shiny material...say aluminum foil..and do this you will probably also get lens flare.
It is very unfortunate that your newly acquired camera is not working properly.