I would try a different mouse, or try the new mouse in a second pc.
I have seen brand new defective mouses.  There are also two major
types of mouse - serial and PS2.  They are not interchangeable and
are often sold with adaptors which enable them to connect to the
'rectangular' 9 pin serial port, the large round connectors or the
small round connectors.
What was wrong with the old mouse?  If operation is erratic, remove
the ball retainer on the bottom and clean the buildup off the
rollers and/or 'shafts'.  It usually appears gray and is just dirt
and dust.

                  Visit our website regularly for FAQs,
               articles, how-to's, tech tips and much more
                          http://freepctech.com