Downloading some ATI drivers from the Acer site didn't help.
Got this from another post.
Go to the Silicon image support website: http://www.siliconimage.com/support/...x?pid=0&cid=0&
download the appropriate DRIVER (not bios) for whatever your computer has - SiI3112 for Non-Raid 2 port SATA 150 controllers worked for me.
Unzip the driver file into a directory.
Go to device manager and "update drivers" for the problem component - on mine it showed Unknown Device. Go to "have disk" and point the browser to the folder with the .inf file for the component. Update the drivers and reboot.
My computer works fine now.