If Excel is not highlighting cells in the formula, enable 'Allow editing directly in cells' and 'Enable fill handle and cell drag-and-drop' in Excel options.

If you Can't type numbers or formulas or enter data into Excel cells then it might be a problematic Add-in causing the problem. Here are some working fixes that may help.

Can't See Columns in Excel. Over the course of a long night, you prepared your spreadsheet. However, when you looked at it the next morning, you find that you cannot see several columns.