Cannot Edit Directly in a Cell

I am running Excel 2007 on Windows XP. I have two problems, which occur in
all excel files I open:
First, I cannot edit anything directly in a cell. I would like to
double-click and edit any cell, but Excel ignores my attempts. I have already
tried disabling and re-enabling the Excel option (under the Advanced menu)
"Allow editing directly in cells." Nothing changed.
Second, when I click on a cell, it will select it and two cells above it.
This only happens half of the time, and I cannot figure out whats causing it.
I have hit F8 numerous times to insure "Extend Selection" is not active.