Hi, I'd go for driver problems  first from what you say.
Try opening up start/settings/control panel/system/device manager and click
on the + next to the mouse . Highlight the mouse (or mice) and remove them.
Restart the computer and the drivers should reload ok.
If that doesn't help, try going to start/settings/control panel/mouse and
see if the settings have been altered in there.
If these things don't help, try replacing the mouse, it could be that the
mouse has seen better days.
Hope this helps.
Michele Sayer

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