The exclamation point is perfectly normal if you are upgrading from LR3, it means that the photo was processed under earlier process versions (the new process version in LR4 is called Process Version 2012). You don't have to "fix" it; you can leave it alone. Alternatively, you can switch to process version 2012 by clicking on the exclamation point, and you will see new develop tools, and most likely the appearance of the image will change. Most people agree that the develop tools in Process Version 2012 is far superior to earlier process versions, but there is a learning curve, and just clicking on the exclamation point will not necessarily improve the photo. Best to find some tutorials about this.
Your screen shows gray thumbnails because your monitor profile is corrupt or invalid. Change your monitor profile to sRGB, the exact procedure depends on your operating system.