Hi,
1. Was it working fine earlier?
2. Which browser you are using?
3. Which Antivirus software installed on your computer?
Follow the below methods:
Method 1: ****
Step 1: Check in Safe mode.
You may also check if the issue persists in safe mode.
Refer:
http://windows.microsoft.com/en-US/windows-vista/Start-your-computer-in-safe-mode
http://windows.microsoft.com/en-US/windows-vista/Advanced-startup-options-including-safe-mode
Now perform Step 2.
Step 2: Perform Clean Boot and check.
To help troubleshoot error message, you can start Windows Vista or Windows 7 by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate software conflicts.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
**http://support.microsoft.com/kb/929135**
**** Please note: After the troubleshooting, make sure to boot your computer to normal mode by following the step 7.
Method 2:
I will suggest updating your anti-virus and malware/spyware protection and removal software and run a full system scan once again.
You can also use the Malicious Software Removal Tool.
The Microsoft Windows Malicious Software Removal Tool checks computers running Windows Vista, Windows 7, Windows XP, Windows 2000, and Windows Server 2003 for infections by specific, prevalent malicious software—including Blaster, Sasser, and Mydoom—and helps remove any infection found. When the detection and removal process is complete, the tool displays a report describing the outcome, including which, if any, malicious software was detected and removed.
You can download it here:
http://www.microsoft.com/security/malwareremove/default.mspx
Hope the above information is helpful.