It seems as if the UxTheme.dll has been modified and/or corrupted. The big matter is this...that DLL is locked and not available for an administrator to modify. The permission policy set on the DLL is TrustedInstaller
There are a few steps
that might work to help solve this problem.
I am going to suggest that the first trial for solving this problem is that we run the Recovery Tool
built-in to the Windows Vista DVD
Here are the steps
-Try doing a Startup Repair
-Use the Command Prompt and run sfc /scannow Tutorial: How to use the command prompt in the Vista Windows Recovery Environment
If this solution does not work, I have two more, so please let me know if this current solution did or did not work.