UDK not opening saved file correctly.

So I feel pretty stupid to have to ask this but I just dont have enough experience with UDK to figure this problem out. Last night I saved out the current level I was working on. So now I have a .udk file and a .upk file. When I opened UDK this morning I imported the .upk file to get all my assets, materials, etc in. Then I tried to open the .udk file and the program crashs ever single time I do this. So I tried open the .udk file first and all I get are lights. Im also not able to load the assets from the .upk file once I have already loaded the .udk file. Sorry if this is a stupid question but not really sure where to go from here. Anyone have suggestions?