Issue with highlighting a cell block

I am very new to Excel and this is probably a very silly question but some how I have turned off my cursor to highlight a cell block. So when I click on a block, it doesn't highlight the edges and when i select multiple cells, it won't highlight those either. Can anyone tell me how to turn it back on??

Thank you!!

KC

Does this happen in just one sheet, or every sheet in a workbook, or in every workbook you open?