I'm on Windows XP Pro with a Pentium4 2.8ghz, 2gb DDRAM, 256mb Sapphire Radeon graphics card.
If I turn off layer visibility my image won't show the change. I have to click on another layer before it will redraw the image. If I make a levels adjustment level and drag a slider while holding alt to show clipping the screen will stay green and black, red and black, or blue and black depending on the channel I adjust until I click on another layer.
5mb JPG images take about 10 seconds to open, flattening the image takes another 5-8 seconds. When I start Photoshop all menu items are greyed out for some arbitrary amount of time yet I can do commands like open by doing the keyboard shortcut.
If I could return this garbage to the store I would, and I'd go back to CS1 and be so much happier and more productive.
First, check here to see if you card falls under the "tested" list. If it doesn't you could disable OpenGL drawing in PS prefs and see if that helps. Definitely make sure all your video card drivers are up to date.
Sorry, forgot to mention that all my drivers are updated. Enabling GPU is greyed out in the preferences.
Tooltips also won't show up no matter how long I hover over something.
I've tried the disallow OpenGL and allow old GPU registry keys and that doesn't work either.