Follow the suggestions listed below for a possible fix:
Method 1: I would suggest you to scan your computer with Microsoft Safety Scanner, which would help us to get rid of viruses, spyware, and other malicious software.
The Microsoft Safety Scanner is a free downloadable security tool that provides on-demand scanning and helps remove viruses, spyware, and other malicious software. It works with your existing antivirus software.
http://www.microsoft.com/security/scanner/en-us/default.aspx
Note: The Microsoft Safety Scanner expires 10 days after being downloaded. To rerun a scan with the latest anti-malware definitions, download and run the Microsoft Safety Scanner again.
Important: While scanning the hard drive if any bad sectors are found, the scanner tries to repair that sector, any data available on that might be lost.
Method 2: Create a new user account and check if you’re able to change the User Account Control (UAC) settings in the newly created account.
Create a user account
http://windows.microsoft.com/en-us/Windows-vista/Create-a-user-account
If the issue does not persist in the new user account, it could indicate that your old user account is corrupted.
Access the link below and follow the steps to repair the corrupt user profile:
Fix a corrupted user profile
http://windows.microsoft.com/en-US/Windows-vista/Fix-a-corrupted-user-profile
