I'm using Excel 2k on XP, SP1...

My problem is that I did something to lock (for lack of a better word) a
particular cell. (No, I didn't do this on purpose.) Now, whenever I click on
another row, Excel highlights all the rows from (and including) that "locked"
cell, to the row on which I just clicked. If I click on a row in just another
column, Excel highlights the range of cells from my "locked" cell to the cell on
which I just clicked. In other words, Excel always makes sure that the "locked"
cell creates a 'range' of highlighted cells from where I really am.

Since I don't know if this is normal, and I don't know what it's called, I don't
know how to look it up in help to see what it is, and how to turn it off.

I tried closing my spreadsheet, then opening it again. Doesn't work. Excel
still remembers my "locked" cell. When I rebooted my PC however, Excel forgot
about the "locked" cell, and I could continue my work.

Is this some normal feature of Excel that I've managed to turn on by accident?
If so, what's it called? And how do I turn it off?

Thanks in advance,

Tom