I use a desk top computer with Windows 7 primarily for emails and using Excel. A problem with using the mouse has started after years of normal use. In Excel, if I click on an empty cell I get one of two results. The normal one illuminates the cell and I can then type an entry into the cell. The abnormal one, illuminates the cell but it has a flashing vertical bar in the cell. I have tried this repeatedly and I never know whether the click will give the normal or abnormal result.
If I click on a cell that has a formula in it, normally the formula appears in the bar above and the result of the formula is in the cell. In the unpredictable abnormal case, the formula appears as usual in the bar but it also appears in the cell rather than the result.
If the cell contains a number, I can normally simply over write that number by typing another one in. However, in the abnormal case, the flashing vertical bar appears in the exiting number and I have to delete the digits of the number before I can put the new number in the cell.