I assume this is Excel and I assume you have not chosen to hide column A.
When you save a spreadsheet it remembers where you were in a sheet so when you open it, you will see what you had on display when you saved it.
On the bottom line of the sheet you will see on the left a set of tabs (usually saying Sheet 1 ; Sheet 2 etc. (Unless you have renamed them). To the right of these, you should have a section of the line with a left arrow, a slider bar and a right arrow. Trying clicking the left facing arrow which should cause the spreadshet to shift to the right and expose your missing column A. Hope this works.
Regards
Torksey