Open Lightroom holding down the ALT Key(Windows)/Opt Key(Mac) and it will give you the window to choose the catalog to open and also it allows you to create new catalog.
therefor, Create a New catalog and save it to the desktop and see if it works.
If it opens with the new catalog, try Open the existing catalog which should be save under the "Picture" folder on your machine.
Let us know if it works.
nothing shows up in the select catalog box. there is nothing there