Have you tried cleaning your system of resource wasting garbage and registry errors? If not run CCleaner and do the Clean and Registry both. Defrag.
Have you installed many graphics driver versions over the time you had the system? If so, uninstall the existing driver, boot to Safe Mode and run Driver Sweeper to remove remnants of any old ATI, AMD, or even Nvidia video drivers it finds. Reboot and install the latest AMD graphics driver.http://www.piriform.com/ccleanerhttp://phyxion.net/item/driver-sweeper.html