mouse won't respond in Excel

[Claudine]

Hi

When using Excel and selecting cells the mouse appears to
go crazy and won't deselect. It becomes highly sensitive
to movement and hurries across the worksheet selecting all
in its path. I have changed mice and have confirmed it is
not the problem. The problem only exists in Excel. The
only way to resolve it (temporarily) appears to be
shutting down. Can't save. Keyboard doesn't respond.

Help required!

Thanks, Claudine