If I understand correctly, the clipping was occurring in Camera Raw? If that was the case, you just click on the triangles in the top corners of the histogram to turn them on or off. As far as Camera Raw not recognizing your camera, for that camera, you need, at least, Camera raw 6.7. When you reinstalled you most likely loaded only 6.0. You need to install that:
No the clipping does not happen in Camera Raw, it is when I open file in Photoshop, not camera raw. And I did instal Camera raw 6.7 but it did nothing. I even tried updating from the Help section and said there were errors. Now I can't even get the program to reinstall. It is a mess! Need help please. Adobe is not helping they just send me to look on my own and won't answer questions!
to get a clean install of PS, you will need to uninstall it again - I know a PIA. Then use the cleanup script, which will remove things your OS uninstaller didn't catch - hopefully the issue you've been having.
Then try and reinstall ACR 6.7 It looks like for that camera, ACR 6.7 might have been a partial build and the full one is ACR 7.1, but that only works with CS6. If you still have problems with opening the files, you might want to try a dng converter and save the files down to a version that CS5 can handle.
if the clipping you're seeing is in PS not camera raw, try turning you gamut warning off. (under the View menu)
as far as I remember, the 5DMKIII was not supported by CS5. Its what ultimately caused me to upgrade to CS6. You can use the free DNG converter to open your MKIII files in older versions of camera raw. I know its not the best workflow, but it will save you the cost of the upgrade.