Help! Ctrl-D in Excel suddenly just pastes the value, not the formula

I do hope somebody can help me!  I've used Excel 2002 since it was
released, and have never met this problem before.

Basically, I have a very simple spreadsheet that maintains running
totals in Column  H - you know, very standard, adds the previous
line's running total to the new data entered in this line, and voila,
calculates the new running total.  The Filling function is obviously a
lifesaver with such a spreadsheet -- until now, I have blissfully been
able to maintain running total accuracy by doing this:

1.  enter the formula for the running total in a Column H cell (i.e.
"=H1+G2-G2").
2. highlight that cell and the other cells underneath it in COlumn H.
3. press Ctrl-D to "fill" those other cells with the FORMULAE of the
correct cell.

It's always worked perfectly. But suddenly this evening, when I press
Ctrl-D instead of pasting the formulae it pastes the value - so I now
have useless spreadsheets with COlumn H just filled with one identical
number, over and over.

I have tried creating a brand new Excel document, but Ctrl-D doesn't
work there either. I've also tried restarting Excel and thenr
estarting WIndows entirely, but still, no joy.

What on earth can I do to make Ctrl-D work again? I am really
concerned and would be ever so grateful for any thoughts.

Hopeful,
Sara Wasson
[EMAIL PROTECTED]