format column cell background in a table if text entered

Jitterbug23 

It's certainly possible.  But for any cells (column C cells, in your example) that already have conditional formatting, the order of the formats may be an issue to deal with after the following steps.

(The assumption below is that you are using a Windows version of Excel; menus for Excel for Mac or the web version may differ.)

Select kcell C2 and extend your selection down as far as needed.  From the Styles section of the Home menu, select Conditional Formatting and click New rule…  In the dialog that appears, click the entry for "Use a formula to determine which cells to format".  In the text box below "Format values where this formula is true:", enter =C2<>"" and click the "Format…" button to select the grey, etc.  Click OK as needed to close the dialogs.