Until yesterday my Windows App Store Icon was still on my start screen. It is now gone and also not listed in my apps. what happened and what can i do to get it back?
Are you sure it isn't in the application list? It isn't listed under Windows Phone Store, but just Store. Look in the S section. I'm betting it will be there.
What hopmedic said, system apps like that don't vanish overnight. (or ever)
You probably already know how to pin, but hold the Store app, and select pin to start.