Sounds like damaged system files. Try SFC to repair them.
The System File Checker tool
To determine whether the issue that you are experiencing is caused by one or more system files that are used by Windows Vista, run the System File Checker tool. The System File Checker tool scans system files and replaces incorrect versions of the system files by using the correct versions.
To run the System File Checker tool, follow these steps:
1.Click Start, and then type cmd in the Start Search box.
2. Right-click cmd in the Programs list, and then click Run as administrator.
3.If you are prompted for an administrator password or confirmation, type your password or click Continue
4.At the command prompt, type the following line, and then press ENTER: sfc /scannow
When the scan is complete, test to see whether the issue that you are experiencing is resolved.
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Mark L. Ferguson MS-MVP 
