Every time I turn on my computer a YImage.dll is not found and it says I need to reinstall it. How can I get this file back on my computer?

This file is apparenlty needed for Yahoo Messenger or for a Nikon supplied software. You can reinstall the software, that needs it or youi can enter the filename into Google or another search engine and you will find places to download it.

There is a third option; to take the program that is trying to load it out of your startup if you don't want it. Go to Start>Run and type MSCONFIG and go into Startup and uncheck the program that is calling it.