Asked here...answered here.
A common cause of this is that you are in "Extended" or "Add" mode.
If you see "EXT" or "ADD" down on the status bar try hitting F8 key a couple
of times.
F8 will will toggle you in and out of Extended mode. SHIFT + F8 will put you
in "ADD" mode.
If you are using a wheel-mouse tap the wheel a couple times.
Also see David McRitchie's "Ghosting" at
http://www.mvps.org/dmcritchie/excel/ghosting.txt
Gord Dibben Excel MVP
