If you are talking about Windows 10 then give this a try:
Simply press the windows key once to open up the "start" menu, without touching anything else type in "Store". If the microsoft store shows up in the list of result, right click on it and select "pin to start" to permanently add it to the tile zone.
I had the same issue after a fresh install of Windows 10. That took care if it. Most applications can be pinned to start that way too