Hi, I've been using Excel for many years. However recently in the past month I think, there has been an odd behavior with the mouse that involves the way it selects cells.

Battery: changed that to a new one to rule out it as a source.
Mouse settings: reviewed every possible setting in both normal and advance dialogues. didn't see anything that relates to my problem.

The problem happens when doing something extremely routine. I want to use the mouse to select, say, 4 cells in a row, with the goal of copying that set of for down one row. For years, I would do this by wishing to select, say, cells I160 through L160. Then I'd simply take the fill handle and drag it down a row. Easy. Something I've probably done 10s of thousands of times.

Lately, and most noticeably today, when I try to select I160 through L160, the selection doesn't "stick". I'll hover over I160, click the left mouse button, and then move the most towards L160, and instead of selecting that range, the selection changes as the mouse covers the cells in between, usually settling on selecting only cell L160.

What the heck happened? This is so incredibly basic I'm sure there is an easy answer, but I don't know what it is so I thought I'd send up a flare. I appreciate any help you can provide.

Thanks