I was using Photoshop CS successfully on my iMac (bought in 2008) until I upgraded from Snow Leopard to Lion and it stopped working. I installed CS5, and it doesn't work well at all; when I try to open and work on an 800 MB file it freezes and sticks and I get the spinning ball continuously. I am currently 4GB RAM. CS5 works great on my husband's computer and he has the same amount of Ram, and he is still using Snow Leopard. I also use Wacom Intuos 3 but the same thing happens with my mouse . I don't know what to do to improve the performance of CS5. Any help would be appreciated. Thanks.