CTRL key in Excel 2007 won't "cherry pick"

I am using Windows XP Media Center SP2 - been using Office XP for years with
no problems. I installed Office 2007 Pro Plus two days ago (added 2007 and
left XP installed, not an upgrade or replacement). All of a sudden now in
Excel 2007 I cannot use the CTRL key to select individual cells not
contiguous to each other. I click on a cell, hold down CTRL and click on
another cell - it acts as if I am not holding down CTRL. Does the same thing
with both right & left CTRL keys.

I checked in Outlook 2007 and I can still "cherry pick" - I can also do it
successfully in Word 2007. I loaded the CD and "repaired" Office 2007 and
rebooted - still cannot get the CTRL key to do what it has done for ages in
Excel 2007. I opened Excel XP and CTRL works exactly like it always has
[successfully].

Any help offered is deeply appreciated.

PS: I have both XP and 2007 Pro Plus installed on my Dell laptop and they
have been peacefully coexisting w/o any problems [like this one] for over a
year.

L B Tague