Disable System Restore
1. Click on the 'Start' button, then right-click 'My Computer.'
2. Select 'Properties.'

3. Click on the 'System Restore' tab in the 'System Properties' window.
4. Click the check box next to 'Turn off System Restore.'
5. Click 'Yes' to confirm.
Update Antivirus Software and Scan Computer
6. Update your antivirus software with the latest version by opening the software and clicking to your 'Update Manager' or to an aptly named 'Update' function.
7. Click on 'Update Now.'
8. Reboot the computer. Press the F8 key after the computer restarts but prior to the appearance of the Windows splash screen.
9. Choose to start Windows in 'Safe Mode.' Press the 'Enter' key.
10. Go to the 'Scan' function of your antivirus software. Click on 'Perform Full System Scan.'
11. Quarantine or eliminate any infected files the scanner finds.
Remove Registry Entries
12. Click on the 'Start' button, then 'Run.'
13. Type 'regedit.' Press the 'Enter' key.
14. Click on 'Edit' in the toolbar. Select 'Find.'
15. Enter each key listed in the Symantec link under 'References.' Highlight the entry, if it is not already highlighted, then right-click on the entry. Select 'Delete.'
16. Click on 'File,' then 'Exit' after you've deleted all keys.
17. Restart the computer. If the 'Critical System Error' message does not reappear, you may re-enable 'System Restore.' Follow the instructions in Section 1, and uncheck the box next to 'Turn off System Restore.'