Acer 5750-6493 running ultra slow

My Acer 5750 recently began running very slow, hanging up on Firefox as soon as a second tab is opened, even though basically most functions still work. I have very few programs loaded and only 10% of the hard drive is full. I have run a number of virus/malware scans, but no hits and no signs of being re-directed to websites, etc. Even with no programs open Physical memory usage is around 40%. I went through some diagnostics and no memory issues were detected. I reset the system a few days, but no improvement. When I tried to reset the system to earlier dates it failed. I tried to do re-install the system, but somehow when I created the recovery disks, I ended up with 4 of them and the computer does not recognize them. Any ideas?