Select Non-adjacent Cells

I've always been able to select non-adjacent cells in spreadsheets, but today noticed that I can't. I need to be able to do so to collect data from one spreadsheet to another for my monthly accounting reports. It makes collection of specific data fast and simple. Without this function, it takes far longer to do reporting and is very un-reliable. With the function working, I click on the cell ranges which are black, leaving the cell ranges which are red alone. We use black and red to identify charges which appear or do not yet appear on our monthly VISA statement.

I select all the black charges along with their corresponding account codes, then double-check the page before copying the non-adjacent ranges to make certain that all of the charge amounts and account numbers which are black on the page are selected and no red ones; then copy and paste the data into another sheet. It often makes collection very quick and easy.

When there are lines interspersed throughout a sheet with black and red charges strewn here and there, it is very easy to select only the black data and skip the red. Doing so by copying the entire range then deleting the red is laborious, and time-consuming.

What has happened to Excel's ability to select non-adjacent cells? Today, I can't select even two separate cells, using Excel's ability to do so by holding down the CTRL key, as I have in the past.

I'm using Excel 2007, on Windows Vista 64 bit; and I've made sure that my Insert function is turned off (thought that might change things?) and my Scroll Lock is turned off (I've bumped that many times in the past and found Excel doing weird things when trying to navigate a spreadsheet with the arrow keys).