Hi, Serene!
You can set cell attributes to Blocked and Hidden, you can Hide row 2 or column 3 (asumming C2 is the involved cell), you can protect worksheet with no protected cells selection capabilities... but you can't avoid the user typing this in another unlocked cell:
=C2 on same worksheet, or =Sheet1!C2 on another worksheet
So, I'm afraid that you can't achieve your goal.
Once a file is open, the data is accessible, directly, indirecty, easily, hardly, but it is.
Regards!