try to scan ur system using your anti-virus or if still not work you need to reset it to its factory default or reformatting your HDD...
How to Format a Computer with Windows Vista
Warning - Formatting hard drive information does not permanently erase the data. Even after a computer has been formatted, deleted files can be easily recovered. If you want to permanently wipe your hard drive by completely overwritting hard drive data, check out WipeDrive.
To format your hard disk during Windows Vista installation, you'll need to start, or boot, your computer using the Windows Vista installation disc or USB flash drive.
- Turn on your computer so that Windows starts normally, insert the Windows Vista installation disc, and then shut down your computer.
- Restart your computer.
- Press any key when prompted, and then follow the instructions that appear.
- On the Install Windows page, follow any instructions that are displayed, and then click Install now.
- If the Install Windows page doesn't appear, and you're not asked to press any key, you might need to change some system settings. To learn how to do this, see Start Windows from a CD or DVD.
- On the Get important updates for installation page, we recommend getting the latest updates to help ensure a successful installation and to help protect your computer against security threats. You will need an Internet connection to get installation updates.
- On the Type your product key for activation page, do one of the following:
- If you are reinstalling Windows Vista, you should enter your product key now.
- If you are not reinstalling Windows Vista, you can skip this step.
- On the Please read the license terms page, if you accept the license terms, click I accept the license terms.
- On the Which type of installation do you want? page, click Custom.
- On the Where do you want to install Windows? page, click Drive options (advanced).
- Click the partition that you want to format and click Format
- If you have more than one partition on this hard drive and want to get rid them to make one big drive again, then select a partition and click on the Delete option for each partition. Once you have deleted all of the partitions, select the Unallocated Space partition and click Format
- When you've finished formatting, click Next.
- Follow the instructions to finish installing Windows Vista, which include naming your computer and setting up an initial user account.
- If you do not want to reinstall Windows Vista, you can cancel the installation at this point and keep your newly formatted drives.