is this a wireless mouse? try changing the batteries maybe.
if wired give the ball a clean.
as its opening files this would worry me.i would run an up to date antivirus and a scan for adware and spyware etc.
do you have and antivirus? if not try click here download,update it and run it.also try adaware and spybot click here click here also update before running them.remove anything they find.