|Why are you trying to copy a cell with numbers and paste it after an = sign? Cells with numbers don't require an equal sign.|
Besides, I don't think you have an issue to resolve, because I don't think you can do what I think are trying.
If you are clicking the cell and simply copying it, you can't paste it after an = sign. When you copy a cell you are copying every thing Excel knows about that cell, including it's formatting, it's address, etc. You can't paste all that info after an = sign.
However, if you click the cell, and highlight what's in the formula bar, or double click the cell and highlight its contents, then you can paste the "text" that you copied any where you want.