Try to reinstall your antivirus software.

1. Check if the antivirus software is compatibe with your computer.
2. Check if the antivirus software is up to date.
3. Double check that you have installed your antivirus correctly.
4. Make sure that the antivirus software is recognized by the computer.
5. Verify the computer does not have any anti-virus software blocking yours.(Check if there are any other anti-virus software on the computer).