Updated Montezuma and lost my site

Help! I did the Montezuma update and now my site is a complete mess. All of my colors and graphics are gone; my 3 columns format has disappeared; widgets are missing, etc. It says that the theme is Installed but incomplete, that the stylesheet is missing. I am not website literate, this was done for me. I do not read or write code and I don't know what a stylesheet is. I have no idea how to fix this or what I am even looking at. I have attached my before and the after. Can someone please help me get this back? Or at least start fixing it by finding what's missing??

Thanks in advance