Lenovo G550 touchpad scroll bar does not work with windows 7.
Have you tried installing the drivers for the touchpad?
The link below will take you to the driver download page for your laptop, scroll down to the section for touchpad and install either the windows 7 32-bit or 64-bit drivers.
http://consumersupport.lenovo.com/en/DriversDownloads/drivers_list.aspx?CategoryID=600154
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